US3868250A - Heat resistant alloys - Google Patents

Abstract

An aluminum-magnesium-silicon alloy with the customary additions for the production of parts such as cylinder heads, for resisting high alternating stressing and also high thermal stressing, wherein the improvement comprises the presence of grain-refined Mg2Si and a component for reducing the solubility of hydrogen.

Description

O United States Patent 1 1 11 1 3,868,250

Zimmermann 1 Feb. 25, 1975 HEAT RESISTANT ALLOYS 3,279,915 10/1966 Fujisawa et a1. 75/147 3,392,015 7/1968 Badia 75/147 [75] Invent: 'F 3,429,695 2/1969 Nakamura et a1. 75/147 Grlmmlmghausem Germany 3,514,286 5/1970 Unai et a1. 75/147 3,666,451 5/1972 [73] Asslgnee' Meschede'Ruhr 3,698,890 10/1972 Bewley 75/147 Germany [22] Flled: June 1972 Primary ExaminerW. Stallard [21] Appl. No.1 260,556 Attorney, Agent, or Firm-Spencer & Kaye [30] Foreign Application Priority Data June 14, 1971 Germany 2129352 [57] ABSTRACT An aluminum-magnesium-silicon alloy with the cus- [52] [1.8. CI 75/147, 148/3, 148/159 tomary additions for the production of parts Such as [5]] '9 Cl Czzc 21/04 Czzf 9 Fozf cylinder heads, for resisting high alternating stressing [58] held of Search 75/147, l48/;,9l593, and also high thermal stressing, wherein the improve ment comprises the presence of grain-refined Mg Si d a c m o ent f0 ed cin the sol bilit ofh dro- [56] References Cited 22 O p n r r u g u y y UNITED STATES PATENTS 2,186,394 1/1940 Spitaler 75/147 9 Claims, 3 Drawing Figures ALTERNAT1NG LOAD NUMBER lei/9 TOTAL 5.14

1 TOTAL 7.4

5 FREE Mg 0 MEASURED VALUES FROM TABLE 8 0 AVERAGE VALUES FROM TABLE 8 Q AVERAGE VALUE FROM TABLE 7 OTHER ALLOYING COMPONENTS TABLE 8 0,98 7,00 /a 51' 0,89 0,92 Mn .50 0,55 (u 0.75 /u Ti 0,33 -a14$ /0 Fe 0,4104% Be BALANCE Al n.b. NOT DETERMINED TABLE 7 M1. "/0 Ti 9'0 Be BALANCE AZ FEHZSIBYS SHEET 1 BF 2 7400 %/v TOT. 7300 S3 1100 m g 7000 Z 2 .900 8 800 g be O E 600 M1 TOTAL 5.|4 g m E 400 300 200 0 1w Z9 TOTAL 7.4

o s 5 FREE Mg 0 MEASURED VALUES FROM TABLE 8 Q AVERAGE VALUES FROM TABLE 8 @i AVERAGE VALUE FROM TABLE 7 OTHER ALLOYING COMPONENTS TABLE 8 TABLE 7 0,98 7,00 0 51' 0,94 0,99 /0 51' 0,89 0,92 /0 Mn 0.36 %/"/n 0,56 0,55 (a 0.5.2 0,55 Cu 0,75 /0 Ti n. b. "/0 72' 0,33 -a4$ /oFe OAS-0,45% 0,0049% Be n. b. %Be BALANCE Al BALANCE AZ n.b. NOT DETERMINED PATENTEDrmmqm K SHEET 2 0f 2 FIG. 2

3.0 3.5 4.0 4.5 5.0 5.5 do 615 in %/1 FIG.3

1 HEAT RESISTANT ALLOYS BACKGROUND OF THE INVENTION The present invention relates to AlMgSi alloys with the customary additives and to a material thereof for the production of parts resisting highly cyclic loads and high thermal stresses, to the use of such alloys and of materials thereof for heat-resistant parts, and to components made of these materials.

As a consequence of the higher requirements placed on a wide variety of different designs at the present time, metallic materials must withstand higher stresses as well. These higher stresses of materials occur at lower and higher temperatures. Changes in the composition of alloys have become, therefore, necessary. Some alloys, among these the heat-resistant aluminum-magnesium-silicon alloys, represent an exception. They have been cast for decades in the same composition.

Investigations for an improvement of aluminum-magnesium-silicon alloys were made almost three decades ago. These experiments related particularly to the improvement of the age-hardenability of alloys with 3% magnesium and 0.8% silicon. Through an addition of cerium the magnesium-silicide could be grain-refined. With further additions of 0.8% zinc and 0.8% manganese alloyed together with cerium, a further improvement was obtained which was, however, not so distinct as that effected by the addition of cerium. This alloy has not been used.

Later, others carried out extensive experiments with extruded aluminum-magnesium-silicon alloys in order to make the quasibinary, the ternary and the beloweutectic compositions usable for heat-resistant purposes. These experiments were not continued although also here the hot-strength inherent in aluminummagnesium alloys was noted and could be improved by other alloying constituents.

These and other numerous experiments have led to the use of aluminum-magnesium-silicon alloys, containing: 2-5.5% magnesium; -l.5% silicon; 00.6% manganese; 0-0.20% titanium, balance aluminum. For heat-resistant purposes, mainly for use as cylinder head material, an aluminum base alloy with the almost equal composition, used by all foundries, of 4.8 5.5% magnesium, 0.8 l.2% silicon, 0.4 0.6% copper, the above manganese content range, balance aluminum, was normally delivered. As per agreement with the purchaser, small quantities of beryllium were sometimes added to these alloys for inhibiting oxidation.

The ranges for the magnesium and silicon contents of these alloys permit a wide variation in the quantity of magnesium silicide which can be formed. Furthermore, magnesium not combined with silicon is found in the alloys. This is shown in Table 1.

Table l-Continued Combined and Uncombined Magnesium SUMMARY OF THE INVENTION An object of the invention is to provide an aluminum-magnesium-silicon alloy especially resistant to thermal fatigue.

This as well as other objects which will become apparent in the discussion that follows are achieved, ac cording to the present invention, by an aluminum-magnesium-silicon alloy having grain-refined Mg Si and a component for reducing the solubility of hydrogen.

GENERAL ASPECTS OF THE INVENTION Toward the end of improving the alloys mentioned in the above BACKGROUND OF THE INVENTION, numerous experiments have been made. These experiments were based on the working hypothesis that aluminum-magnesium-silicon alloys for withstanding high stresses, in particular for withstanding alternating thermal stresses, must possess magnesium and silicon contents equilibrated to each other, and that the free magnesium content umcombined with silicon must not exceed beyond limits the solid solubility of magnesium in aluminum at room temperature.

Especially the use of the alloys mentioned in the BACKGROUND OF THE INVENTION for cylinder heads gave rise to the recognition that cracking caused by the temperatures prevailing in the combustion chamber occurs earlier at higher magnesium contents. A reduction of the magnesium content to lower concentrations should also be of advantage for increasing the solidus point of the alloys.

Besides establishing the influence of magnesium content, numerous investigations were made for establishing the influences of various other alloying constituents. Prior to casting, the melts were extensively degassed and only such elements were added, the addition of which was known not to increase the solubility of hydrogen. Furthermore, the solidus points in the aluminum-magnesium-silicon system were not to be decreased considerably, and in addition the grain refinement of the structure was to be improved. Combined with the component for reducing the solubility of hydrogen, it is important for obtaining the best grainrefinement in the Mg Si, i.e., for maximizing the fineness of the Mg Si grains, that an extra measure be taken to assure no hydrogen evolution occurs during the time that the alloys are cooling from the molten condition to solidification to disturb the formation of a fine microstructure. Such evolution is prevented by the intensive degassing at the time of casting. An equilibrium condition, under which no hydrogen evolution occurs, is obtained right at the time of solidification. This equilibrium condition corresponds to a certain maximum amount of hydrogen dissolved in the melt at the time of casting.

lt was found that, when casting aluminum-magnesium-silicon alloys in permanent molds having a temperature of 300 C, a finer distribution of Mg Si is obtained, the smaller the magnesium content of the alloy is that is not combined with silicon, and that through an increased manganese content in the absence of cerium and zinc, a still finer Mg Si is obtained which at low magnesium content is recognized only at a very high magnification microscopically as a very fine precipitate. The influence of manganese on mechanical properties is consequently outstanding at room temperature and elevated temperatures as shown in Table 2. The tensile test specimens of Table 2 were subjected to a stabilizing annealing before testing. The stabilizing annealing causes a major separating of solid solution crystals into separate phases and thus represents a softening anneal. Growth changes are prevented by this. Decisive The specimens for obtaining the data specified in Table 2 had a length of 22 cm and an original diameter of 2.2 cm over the whole gage length. They were made by chill casting at casting temperatures of approximately 720 to 750 C. The diameter over the gage length was obtained by turning on a lathe from the as cast diameter of 2.2 cm to 1.6 cm. The castings had a riser over their entire length. The mold, open at the top, was filled from one side through a gate. The chill was horizontal and had a temperature of 300 C.

The addition of manganese should not exceed the maximum solid solubility in the aluminum-manganese system, but it should also not be lower than 0.6%.

The grain refining of the structure of Mg Si through the action of manganese has nothing in common with the forming of pointed, needle-shaped iron aluminides by manganese in aluminum-silicon-alloys with low magnesium-contents from up to approximately 0.6%. It is true that in Al-Mg-Si alloys with Fe-contents of isamajor stabilizing against the effects oflater heating. 1.25%, Mg Si can be refined by higher manganese- When used, the material experiences no further contents, but a forming of the iron aluminide into a changes. The stabilizing annealing effects an annealing, multi-substance compound cannot occur as is the case a stabilizing, and a stress relieving. with aluminum-silicon alloys. These alloys have low In the Tables, the following symbols are used: elongation and strength properties, as shown in Table 0 yield strength 3. 0,, breaking strength The pointed iron aluminide structure found in the 5 elongation aluminum-magnesium-silicon alloys of Table 3 is not HB Brinell hardness. prevented in the ternary aluminum-silicon magnesium Table 2 Charge Analysis in Tests at 20C Tests at 300C Tests at 400C No. kp"/mm 7r kp"/mm kp' lmm 7c kp*/mm Mg Si Mn Fe 0' 17B 5 HB (701 B 5 11.2 's .5

Avg. value 7.7 17.1 6.1 54 5.9 8.6 62.1 2.8 4.5 65.0

Avg. value 20.7 14.6 56 5.6 9.3 38.1 4.1 6.2 78.0

Avg. value 10.1 21.6 6.5 64 7.4 11.1 27.3 4.1 6.2 84.0

Avg. value 12.5 26.7 9.6 70 8.9 12.7 48.6 5.3 7.8 83.4

Avg. value 13.0 23.3 5.2 72 9.6 13.8 21.8 4.1 6.7 115.2

Avg. value 13.7 23.5 4.4 9.5 14.0 20.5 5.1 7.9 97.0

p ponds Further concerning Table 2 and subsequent Tables herein, the test bars had a gage diameter of 16 mm and a gage length of 80 mm, i.e., 5-fold diameter. The elongation measured in the tensile testing machine during the tension test until break of the test bar is the elongation 8 stated in per cent of the original length of 80 alloys with approximately 13% silicon and 6% magnesium by an increased addition of manganese. Such experiments show in regard to the strength properties also no outstanding technical progress for a combination with manganese; they show also that in an application of manganese in the presence of large quantities of silicon and larger quantities of magnesium the effect of manganese is not comparable to that in aluminumsilicon alloys with up to 0.6% magnesium or without magnesium. See Table 4.

shows the improvement of strength properties caused by manganese in alloys lying approximately in the melting valley between the ternary, magnesium-rich and Table 3 Charge Analysis in Tests at 20C Tests at 300C Tests at 400C No. kp/mm kp*/mm kp/mm 7r ltp/mm Mg Si Mn Fe (T 5 HB 0.2 's s 0.2 n s Avg. value 8.8 17.4 3.6 57 5.3 9.2 44.5 2.9 5.0 80.0

Avg. value 9.3 16.2 2.5 63 5.5 10.3 10.4 3.6 6.5 65.0

Avg. value 10.6 22.6 4.9 71 8 3 12.1 37.9 4.1 6.7 98.2

Avg. value 10.4 18.5 3.0 69 8 5 l2 3 7.3 4.2 7.2 73.4

Avg. value 12.4 21.5 3.4 76 9.4 14.0 14.9 3.6 6.2 64.6

Avg. value 14.0 18.3 1.5 87 9.2 14.2 4.9 4.1 7.9 83.2

' p ponds Table 4 Charge Analysis in 7: Tests at C Tests at 300C Tests at 400C No. kp"/mm 7r llfp /mm kp"'/mm 7: kplmm Mg Si Mn Fe 0' a, 8, B (T a, 5 a o 8 Avg. value 9.5 16.9 2.9 59 3.8 7.6 11.6 2.4 5.0 20.0

Avg. value 10.7 17.0 2.2 67 5.6 9.2 11.2 2.7 4.2 20.0

Avg. value 10.7 11.9 0.9 70 3.0 8.8 1.8 2.9 64 3.0

Av. value 10.6 14.2 1.6 71 6.3 8.4 3.4 3.2 5.8 7.2

' p ponds After these investigations it was, therefore, astonishsilicon-rich eutectics of the aluminum-siliconing that at very high magnesium-contents of approximately 9 10% and silicon-contents of approximately 3% at free magnesium-contents between 3 and 4% (magnesium not bound to silicon). also at higher ironcontents of 1.20%, iron-needles no longer occur, insofar as higher manganese-contents were added. However, in the presence of high quantities of iron, no considerable changes of strength properties have been caused. 1n the alloys with low iron-contents there is found by the manganese alloying, besides a strong refining of grain structure, a considerable increase of strength properties in connection therewith. Table 5 magnesium system and preferably on the side rich on magnesium, and which have silicon-contents lower than those of the quasi-binary eutectic with 13% Mg si. Preferably silicon-contents between 2.5 and 4% and at most 11% magnesium should be alloyed in the presence of manganese.

The investigations were extended to alloys with silicon-contents of 2% and magnesium-contents of 4%. The strong refining of Mg Si by manganese is obtained here as well. I

With a Cu-content of 1% both in alloys poor on manganese and rich on manganese, Mg Si is coarsened again. 1t is most coarse in the alloys poor in manganese. Table 6 shows that a Cu-content increases strength properties, but that elongation properties are strongly decreased. The strength properties of Cu-free alloys with their higher magnesium-contents not bound to silicon, were not attained. At approximately 4% magnesium and 2% silicon, the alloy contains only 0.55% magnesium not bound to silicon. The machinability of castings from these alloys is worse.

Further results were obtained on investigation of the influence of nickel. Similarly to manganese, nickel contents of about 1% in aluminum show the lowest hydrogen solubility in the molten state. This composition was, therefore, also selected for alloying investigations. It was found that contrary to copper. a 1.5% nickel content gives a very fine magnesium-silicide and that the magnesium-silicide coarsening influence of copper is neutralized in the presence of nickel.

The investigation of tearing strength properties showed that the stabilized alloys, when the magnesium content exceeds 4%. possess low elongation properties. and that the aluminum-magnesium-silicon alloys must contain, in the presence of nickel and/or larger quantities than 0.2% copper, less than 4% magnesium.

Table 5 Charge Analysis in 7: Tests at 20C Tests at 300C Tests at 400C No. kp lmm kp lmm kp"/mm kp"/mm Mg Si Mn Fe a o 8 HB 0,, 6 01, 0,, 8

Avg. value 14.9 24.4 2.7 92 8.8 13.2 25.7 3.6 6.1 74.8

Avg. value 18.1 27.3 2.6 96 11.7 15.9 24.5 4.8 8.5 61.6

Avg. value 12.0 20.0 1.9 79 8.7 12.8 27.5

Avg. value 13.9 25.3 2.8 85 9.4 13.5 21.8

Avg. value 15.8 25.0 3.3 96 9.3 14.6 19.7 4.1 7.4 83.6

Avg. value 18.1 24.1 2.3 103 10.8 16.2 5.9 5.1 8.1 65.2

p ponds Table 6 Charge Analysis in Tests at C Tests at 300C No. kp"lmm kp"'/mm kp/mm Mg Si Mn Cu Fe M a 8,, HB 0' 0' 6 Avg. value 8.1 17.7 5.4 54 4.4 7.7 39.2

Avg. value 8.7 18.6 4.9 4.9 7.5 52.0

Avg. value 10.3 18.4 3.0 65 6.0 9.1 35.4

Avg. value 10.8 19.9 3.4 68 6.1 9.6 39.6

' p ponds BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a graph of alternating load number versus the percentage of free magnesium in an alloy.

FIG. 2 is a graph of the percentage of silicon in an alloy versus the percentage of magnesium and shows the field of free magnesium contents between I and 3%.

FIG. 3 is a cross section through a portion of an aircooled cylinder head according to the invention.

.DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred elements for reducing the solubility of hydrogen in the melt above 700 C are manganese and nickel.

The available results were applied to investigations of cylinder heads. The quality of service to be expected from an alloy used to make a cylinder head was measured in terms of "alternating load number." which is measured as follows.

On a heatable and coolable test stand, those portions of a cylinder head as are most endangered. being nearest to the combustion chamber. are heated for approximately 60 seconds from a temperature of I to 300 C and then cooled in 60 seconds to I00 C again. This effects a change of load. The test on the test stand is carried on until crack formation and then on until the crack has progressed through the wall where it is located. The number of load changes supported by the cylinder head until crack formation and until crackthrough yields alternating load numbers, which serve as an indicator of the ability to resist thermal fatigue.

FIG. I shows among other things the alternating thermal stress tests of cylinder heads made of the customary alloy AlMg5SilCu0.5 per Table 7. The cylinder heads of Table 7 were taken from the normal production in a period extending over several months. There resulted an average alternating load number of 716 until crack formation and 769 until crack-through.

Cylinder heads cast from the material of the invention and showing a fine grain structure were likewise tested. FIG. I and Table 8 show the resulting alternating load numbers. It can be concluded from the investigations that with a silicon content comparable with the customary alloy. and with the customary addition of 0.5% Cu, alloys with high magnesium contents have a considerably shorter operating life even with an additional manganese-alloying. In comparison with the results for the customary alloy (see FIG. I and Tables 7 and 8). the alloys with higher manganese content show a distinct improvement. The graph in FIG. I shows an almost linear dependence between alternating load number and magnesium content and the possibility of a maximum improvement of I00% by the invention. The alloy used for cylinder head No. 3 in Table 8 and FIG. I possesses a free (i.e., not present in Mg si) magnesium-content of approximately 5.7%; the alloy of head No. 2 has a free magnesium-content of 3.77%; and the alloy of head No. I has a free magnesiumcontents of only 2.85%. The alloys of heads No. 4 and No. 5 in Table 8 contain only about 0.9% free magnesium. The alloy of head No. 5 endures after the additional alloying of manganese considerably higher thermal loading. Comparison with the alloys of Table 7 shows the high thermal stress endurance obtained by the reduction of the free magnesium content. The free magnesium content of the alloys Nos. 4 and 5. being 0.9%, is very low. The machinability of these alloys was worse on a production line. The free magnesium contents should be more than We.

The alloys of the invention can also be used as wrought material, if the Si-content is at least 1%.

All investigations show that the free magnesiumcontents of the aluminum-magnesium-silicon alloys for obtaining high endurance, specially against alternating thermal stresses, should be between I and 4.5, preferably at 3.0%, a decrease of free magnesium to less than 1% being possible only for castings that are machined with special tools adapted to the alloy. In the presence of more than 0.6% Mn the preferred 3% free magnesium can go up to about 4.5%.

n.b. I not precisely determinable Table 8 fiyylinder Head Analysis in Z lclterriating load Mg 51 Mn Cu Fe Ti Be C 'ick Crackformation through I 4.55 0.99 0.91 0.50 0.42 0.15 0.004 1450 I600 I350 1500 4 4.4 2.08 0.02 0.17 0.20 0.15 0.004 I040 60 930 I030 n.b. H

5 4.3 L88 0.78 0.15 0.21 0.15 0.004 I380 I590 I380 I420 I360 I410 1|.b. not precisely determinable During the further development of the alloys of the cylinder head in FIG. 3 from an alloy poor in mangainvention and of their applicability. it has been estabn e ha i thg composition lished by thennal alternating stress investigations that, 03% M within the range of the limits of the invention. alloys 51% Mg with the following alloying constitutents have particu- [3% Si larly favorable properties for enduring high- 004% Be temperature alternating stresses and a particularly low b I M d t t t I cracking-tendency in engine operation: a an cus (imary con amman ected to an alternating thennal stress rnvestrgatron after cooling the permanent mold with about 700 cm 70% Ms H O in the area of the spherical cap ll. The cooling 8:: I a was carried out by flowing the water through a metal 38:83?? mold core abutting against the spherical cap I1 and other damn having cylinder inserts protruding into the inlet channel will however 015% maximum l2'and the outlet channel 13. The cooling effect pro- -vided by the cylinder inserts provides an additionally mfzztirr'isiiizlutmlgltzmnl;rlductgaozzgyn 0 improved microstructure in the web 14, which is the silicon be contained in the alloy. A special importance rnost highly stressed portronof the head. The alterna tis. in his insmnce attributed to the proportioning of mg load number was approxrmately 450 for the start of he manganese on which the increase of crack resisv crackrng of theweb area between the Inlet and outlet lance in engine operation depends channels. add tionally In FIG. 3. axes 15 16 and l? are Thc p 1 alloy sckcdon results in panicularly 4 axes of cylindrical symmetry for. respectrvely, the Inlet favmablc mechanical propcnies But a" anoys both channel 12. the spherical cap II. and the outlet chanthose numed first. and those selected now, yield especially improved mechanical properties and to the pres- EXAMPLE 2 ent time. the best crack resistance-against temperature changes. if the endangered or highly stressed areas of Cylmde' headsj of the alloy m Exa'rfple l the cast body are subjected during the solidification to showed bemg f wnh Inc's m a cooling additional to the cooling received by other same an alemamg load number of areas of the bod The behavior of allo free of manganese shows in cylinder heads 30 to 50 of the durabil- EXAMPLE 3 ity achieved in cylinder heads made of alloys contain- Cylinder heads of the manganese rich alloy with the i manganm, composition FIG. 2 shows the range of preferred alloy composi- Mn tions wherein only I to 3% free magnesium (not bound 6o 44% g to silicon) is present. 19% Si Further illustrative of the invention are the following 0.004%- Be E l balance Al and customary contaminants, were subjected, after cooling as in Example 2. to an alternating EXAMPLE I 5 thermal stress test and yielded an alternating load num- Cylinder heads of the type illustrated by air-cooled ber of [.550 to crackthrough.

EXAMPLE 4 Under a more aggravated alternating thermal stress test consisting of a more rapid change of heating and cooling, cylinder heads according to Example 2 gave the reduced alternating load number of 650.

EXAMPLE 5 Cylinder heads from alloys according to Example 3, tested according to Example 4, gave the alternating load number of 1,200.

EXAMPLE 6 EXAMPLE 7 Cylinder heads made from the alloy 0.85 7r Mn 4.7% Mg 1.7% Si balance as in Example 2, were tested on the test-bench for alternating thermal stresses according to Example 4 and endured 1,221 alternations of stress.

EXAMPLE 8 Cylinder heads of the alloy according to Example 7 with only 0.3% Mn, tested on the test-bench for alternating thermal stresses as in Example 4, endured only 430 alternations of stress.

Table 9 Strength properties of the different alloys in the border of the spherical cap of the cylinder heads.

As per Alternating Mechanical properties at 20C example load number Yield Breaking 7( Brmell Stress Strength Hardness kp"/mm kp"/mm kp*/mm 01,, HB

' p ponds The further development of the present invention is dedicated to showing a way of how the ability to endure high thermal stresses, particularly in cylinder heads cast from the aforementioned Al-Mg-Si alloys of the invention, can be considerably improved for obtaining a marked increase of engine operating life, alternating thermal stress endurance and considerably increased durability of sealing surfaces. This is done particularly by increased hardnesses of sealing surfaces, giving also an improvement of the compression chamber seal between cylinder block and cylinder head. So far, the sealing surface durability, which is connected with the Brinell hardness of the alloys, could not alone be considerably improved by concentration increases in the alloy, without at the same time reducing strongly the ability to endure thermal fatigue in cylinder heads made from the alloys.

Especially for thermally highly stressed pieces, such as engine cylinder heads, it has so far been thought that the thermal treatment should consist only of a kind of stabilization annealing and that this cannot be improved, but only be deteriorated, by other treatments, particularly solution treatment alone or a solution treatment, and a subsequent age-hardening. which is customary for all other alloys. It is known that piston alloys for the prevention or reduction of increase in volume are homogenized at 500 C, with subsequent age-hardening, and annealed once more at temperatures of 250 C in the softening area, in order to attain complete growth resistance and freedom from stresses. However, the solution annealing treatment is not the rule for piston alloys, and it has been shown that also an exaggeratedly long annealing at C from 16 to 40 hours, without solution treatment, is sufficient for stabilizing or prevention of growth. Beside that, temperatures of approximately 220 C have also been applied for annealing treatments alone.

The result of these thermal treatments is that alloying components come strongly out of solid solution. Thereby either maximum Brinell hardness properties with strongly decreased elongation properties or else very low Brinell hardness properties are obtained.

The intended further development of the invention involves subjecting the castings to either a solution treatment alone or to a solution treatment and subsequent age-hardening without exceeding the hardness maximum.

Investigations with this process have shown that a considerable improvement of all properties important for resistance to thermal fatigue, especially sealing surface hardness, is obtained, without disadvantage, with the applied thermal treatment. The results of such investigations are listed in Table 10 and become evident from the Examples of alternating thermal stressing of cylinder heads. Shown are the Brinell hardness properties and in individual cases strength properties in the border of the spherical cap of the cylinder heads. [I was found that either a homogenizing or solution treatment must be applied or a solution treatment with subsequent age-hardening without exceeding the hardness maximum of the alloy.

From these results, it can be seen that the investigated alloys show after the treatment according to the invention considerably higher properties, particularly for the sealing surface hardness, as compared with their original properties, and that they endure at the same time higher alternating thermal stressings. The Examples show that the Brinell hardness properties after a stabilizing annealing are low.

In view of these results it is shown that cylinder heads treated according to the invention, even those with a higher Mn-content have a considerably longer durability and that the sealing surface hardness is increased. The cylinder heads from such alloys, listed in the following Examples, particularly Cu-containing alloys, show that the alternating load numbers are considerably increased by the application of the thermal treatment of the invention. This important improvement was not to be foreseen at the present state of the art.

Table Strengthproperties of permanent mold (gravity die) test bars according to the German Air Standard LN 29 531 with a diameter of 22 mm from the manganese-containing Al-Mg-Si alloy without and with copper Average values from two test bars each Mechanical Properties Composition in Heat treatment a 0' 8,, HB

and quench Winks Cu Be Mg Si Mn Fe Ti kp*/mm k 7, q A oy Designation 411/1 0.02 0.004 3.9 0.9 0.85 0.20 0.16 Stabilizing annealin air 10.1 22.9 10.6 66.5 l2"S65C/H O 10.5 25.1 19.6 68.5 12"565C/H,O 17.8 29.4 15.8 85 +6"l55C 12"565C/H,O 19.4 29.5 14.1 83 +6"l75C 41l/l 0.84 0.005 4.0 0.89 0.85 0.20 0.16 Stabilizing Cu annealing/air 11.4 21.0 3.8 72.5

12"565C/H2O 12,9 2 ,9 & 75 l2"565C/H2O 25.5 33.3 6.2 110 +6"155C 12"565C/H-O 25.5 6husroc 2 36.7 8.6 103 p=p0nds EXAMPLE 9 EXAMPLE 11 Investigations for cylinder heads of an alloy having a With the following alloy in identical cylinder heads composition according to Examples 9 and 10, the following results were obtained.

0.9 71 Mn 3.9 v. Mg 0.9 7: Si 71 Cu Z M 0.18 '1' Ti t 1.5 7r Si 0.24 71 Fe I s Ni 0.004 Be Cu Balance Al '7 Ti Heat treatment and quench h 0.25 7r Fe 12 565C/Hz 12565C/H,() +6"155C g- 9 ,5 Alternating o I. 0

Heat Stabilizing 12 565 C/H.O 12 565 C/H-,O load number 1751 Treatment Annealing z 6"175C HB kponds/mm 80 83 Ahemming Properties from 00.2 13.0 kp"/mm 18 2 kp"/mm load number 1642 1700 1930 the border of the 08 27.0 kp*/mm 27.2 kp/mm clyinder head 85 10.0 71 8.8 71 HB spherical cap HB 80 kp"/mm 83.0 kp*/mm kp"/mm 74 93 102 p ponds p ponds The Brinell hardnesses of cylinder heads made from this alloy were between and kiloponds/mm after stabilizing annealing. EXAMPLE 12 50 EXAMPLE 10 Further investigations of cylinder heads made of the Investigations of cylinder heads made of an alloy with followmg alloy g the following results:

0.9 7: Mn 3.9 1 Mg 0.9 7c Si 0.8 1 Cu 0.18 Ti 0.32 Z Fe 0.004 Be Balance Al.

Stabilizing l2"565C/H O Heat Treatment Annealing l2"565C/H,0 6"175C Alternating load number 1275 1570 2095 HB kp"/mm 7| I04 Properties from 00.2 12.0 kp'lmm 16.8 kplmm 27.8 kp/mm the border of the EB 18.4 kp"/mm* 32.6 kp"/mm 33.5 kp/mm" s herical cap of 65 2.9 1 5.4 l 6.6 1' tlie cylinder head HB 71 kp*/mm 110 kp'lmm 108 kp'/mm p ponds .22..

The results ofthe Examples 9 12 reflect the essence of the invention in two respects; firstly, the established thermal treatment removes the influence of unfavorable higher magnesium contents; secondly, after the solution treatment, without disadvantage to the ability to endure alternating thermal stressing, the hardness properties can, even with an increase of the Mgconcentration, be increased considerably, without thereby reducing the resistance against alternating thermal stressing of the cylinder heads.

As shown by Examples 9 12, a solution heat treatment alone can be sufficient, while a subsequent aging can lead to the obtaining of other desired properties.

such components further materials with particularly fine structures. This task is accomplished by the invention in such a way that in an Al-Mg-Si alloy, for the indicated purpose, cobalt or chromium or a combination of the two elements act as elements for reducing the solubility of hydrogen to replace completely or partly the manganese content of 0.6 to 2.0% indicated for other alloys of the invention. The replacement is to be on the basis of equivaleiit numbers of gramatoms. Preferably at least 0.1% Co and/or at least 0.6% Cr is present. In this manner, a grain refining of the structure of components is attained which lends to these components additional outstanding properties. Thus, there can be found in the structure in the case of chromium larger islands with very fine Mg Si. Moreover, the resistance of components, e.g. of cylinder heads, made of Al-Mg-Si alloys, which contain within the indicated limits besides manganese partly cobalt and/r chromium, is excellent.

Also vanadium and molybdenum can be used as elements for reducing the solubility of hydrogen. They replace the manganese content on the basis of equivalent numbers of gram-atoms. At least 0.1% V and/or at least 0.1% M0 is preferably present in such alloys.

Table 11 shows the effect of Cr, Co, V, and M0 in alloys of the invention. Charge Nos. 850 and 2606 are presented for purposes of comparison.

TABLE 1 l Strengnth values determined using chill-mold rod castings according to German Aviation Standard (Luftfahrtnorm) LN 29531 with 22 in diam; average of three values; influence of Cr, Co, V, and Mo.

Works Analysis in Heat Treatment Mechanical Values Alloy No. 0 0,, H8

or Charge Cu Be Mg Si Mn Fe Ti kp/mm kp lmm 850 Stabilizing (s. Tab.2) n.b. 3.6 1.04 0.22 0.31 n.b. Annealing 7.7 17.1 6.1 54

2606 0.90 0.003 4.4 1.52 0.01 0.17 0.22 Solution Heat 19.7 28.8 6.2 97

Treatment 6 hrs at 175C 0.1% Co 0.88 0.005 4.7 1.45 0.01 0.23 0.19 do. 20.1 31.5 8.5 102 Thus, 1n Example 12 where there is a high free Mg con- 1t preferred to use technically pure aluminum. Pertcnt, a solution heat treatment alone can give very recentages here1n are 1n percent by welght unless indispectable properties. In contrast, Examples 9 -11 show that. for a lower free Mg content, an aging in addition to the solution treatment can be of advantage. Then, it remains to be noted that, when a very high Brinell hardness is required for sealing surfaces, for example for surface 18 in H6. 3, an age hardening can be of advantage as shown, for example, in Example 11.

The present invention also leads to the further development of alloys for components which are subjected to maximum alternating thermal stresses, particularly for cylinder heads for combustion engines, the materials for which are based on the Al-Mg-Si alloys of the invention. This further development aimed at finding for cated otherwise.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

1 claim:

1. A high-strength manganese-containing Al-Mg-Si alloy having a free magnesium content of 1.5 to 4%, said alloy consisting essentially of 0.6 to 1.8% manganese, 2 to 7% magnesium, 0.6 to 2.5% silicon, 0.1 to 0.3% titanium, and having been subjected to one of the following steps (a) and (b):

a. a solution treatment up to 565 C maximum;

b. a corresponding solution treatment with subsequent age-hardening at temperatures not exceeding the hardness maximum.

2. An alloy as claimed in claim I, said alloy containing up to 1.5% Ni, up to 3% Cu, up to 0.1% beryllium, and at most 0.6% Fe.

3. An alloy as claimed in claim 1, said alloy containing manganese only in the quantities up to 1.2%, magnesium from 3.0 to 4.5%, silicon from 0.8 to 1.2%, and copper from 0.2 to 1.0%.

4. An alloy as claimed in claim 1, the magnesium content of said alloy being from 4.5 to 7.5% and thesilicon content of said alloy being 0.8 to 2.5%.

5. An aluminum-magnesium-silicon alloy consisting essentially of 0.6 to 4.5% silicon, 2.5 to 11% magnesium, and aluminum, wherein the improvement comprises l to 4.5% free magnesium and at least one material selected from the group consisting of manganese at 0.6 to 1.8%, cobalt, chromium, vanadium. and molybdenum, where the sum of the gram-atoms of manganese, cobalt, vanadium, and molybdenum lies in the gram-atom range equivalent to 0.6 to 1.8% manganese.

6. An alloy as claimed in claim 5, said alloy containing at least one element selected from the group consisting of cobalt at at least 0.1% and chromium at at least 0.6%.

7. An alloy as claimed in claim 5, said alloy containing up to 1.5% Ni, up to 0.5% Cu, and at most 0.6% Fe.

8. An alloy as claimed in claim 5, said .alloy containing 3% free magnesium.

9. An alloy as claimed in claim 5, said alloy containing at least one element selected from the group consisting of vanadium at at least 0.1% and molybdenum at at least 0.1%.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,250 Dated February 1975 lnventofls) Paul Zimmermann It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Columns 9, 10, 11 and 12 as shown on the attached pages should be added:

Signed and Scaled this sixteenth D 21) 0f September 1 9 75 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmissimn-r uf I a Thu/WNW!" 9 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a graph of alternating load number versus the percentage of free magnesium in an alloy.

FIG. 2 is a graph of the percentage of silicon in an alloy versus the percentage of magnesium and shows the field of free magnesium contents between I and 3%.

FIG. 3 is a cross section through a portion of an aircooled cylinder head according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred elements for reducing the solubility of hydrogen in the melt above 700 C are manganese and nickel.

The available results were applied to investigations of cylinder heads. The quality of service to be expected from an alloy used to make a cylinder head was measured in terms of alternating load number. which is measured as follows.

On a heatable and coolable test stand. those portions ofa cylinder head as are most endangered. being nearest to the combustion chamber. are heated for approximately 60 seconds from a temperature of I to 300 C and then cooled in 60 seconds to l00 L again. This effects a change of load. The test on the test stand is carried on until crack formation and then on until the crack has progressed through the wall where it is lo cated. The number of load changes supported by the cylinder head until crack formation and until crackthrough yields alternating load numbers. which serve as an indicator of the ability to resist thermal fatigue.

FIG. I shows among other things the alternating thermal stress tests of cylinder heads made of the customary alloy AlMgSSilCu0.5 per Table 7. The cylinder heads of Table 7 were taken from the normal production in a period extending over several months. There resulted an average alternating load number of 716 until crack formation and 769 until crack-through.

Cylinder heads cast from the material of the inven- Page 2 tion and showing a fine grain structurtwere likeuisc tested FIG. I and Table 8 show the resulting alternating load numbers. It can be concluded trom the ll'l' LMlgations that with a silicon content comparable with the customary alloy. and with the customary addition at 0.5% Cu. alloys with high magnesium contents have a considerably shorter operating life even with an additional manganese-alloying. In comparison with the results for the customary alloy (see FIG I and Tables 7 and 8 t. the alloys with higher manganese content show a distinct improvement. The graph in HG. I shows an almost linear dependence between alternating load number and magnesium content and the possibility of a maximum improvement of 100% by the invention The alioy used for cylinder head No. 3 in Table 8 and FIG. I possesses a free i.e.. not present in Mg Si l mag nesium-content of approximately 5.71'. the alloy of head No. 2 has a free magnesium-content of 3.77 and the alloy of head No. 1 has a free magnesiumcontents of only 2.85%. The alloys of heads No 4 and No. S in Table 8 contain only about 0.9! free magnesium. The alloy of head No. 5 endures after the additional alloying of manganese considerably higher thermal loading. Comparison with the alloys of Table 7 shows the high thermal stress endurance obtained by the reduction of the free magnesium content. The free magnesium content of the alloys Nos. 4 and 5. being 0.9% is very low. The machinability of these alloys was worse on a production line. The free magnesium contents should be more than Vi.

The alloys of the invention can also be used as wrought material, if the Si-eontent is at least li All investigations show that the free magncsiumcontents of the aluminum-magnesium-silicon alloys for obtaining high endurance. specially against alternating thermal stresses. should be between 1 and 4.5. prefe rably at 3.0%. a decrease of free magnesium to less than 1% being possible only for castings that are machined with special tools adapted to the alloy. In the presence of more than 0.6% Mn the preferred 3% free magnesium can go up to about 4.5%.

Table 7 Cylinder Head Analysis in 1' Alternating load No. No.

Mg Si Mn Cu Fe Crack Crackforrnation through I n.b. 709 2 5.06 0 )4 0.36 0.5 3 0.45 639 670 3 E94 M0 4 940 I050 S 450 640 6 5 I) 0.99 0.36 0.51 0.44 775 877 7 707 R72 8 574 736 9 M0 66 l0 n.b. J l l 830 H 12 n.h. I l3 5.": 0.95 0.36 0.55 0.43 n.b. 720 I4 n.b. 660 IS (1.). 6'" l6 n b. (Kl Average values 5 i4 096 0.36 U 54 0 44 Ho '1! rib. not precisely determinable Page 5 Table 8 (ylmder Head Analysts in .t Alternating load N Nu Mg Si Mn Cu Fe ll Be Crack (racl.-

formation through I 4 55 0.99 0.91 0.50 042 0.15 0 004 t-tiu I600 ["0 1500 2 5 Hi0 0.92 0.50 0.32 ti l5 0.004 ttt'ti H90 I200 I224 3 '.'.4 0.98 0.89 0.55 0.33 0 l5 0.003 n.h lhtl n.b. 335

4 4.4 2.08 0.02 0.!7 0.20 (H5 ll 004 I040 l I00 930 I030 n.b. l [00 S 4.3 L88 0.78 0.l5 0 21 015 0.004 I380 i590 I380 i420 I360 MW ".0. not precisely determinable During the further development of the alloys of the invention and of their applicability. it has been established by thermal alternating stress investigations that, within the range of the limits of the invention. alloys with the following alloying constitutcnts have particu- 0.0 0.05! other elements individually. total however 015; maximum Balance aluminum and customary contaminants. on the condition that only l to 3% magnesium unbound to silicon be contained in the alloy. A special importance is. in this instance. attributed to the proportioning of the manganese on which the increase of crack resistance in engine operation depends.

The proposed alloy selection results in particularly favora le mechanical properties. Eat all alloys. both those named first. and those selected now. yield especially improved mechanical properties and to the present time. the best crack resistance against temperature changes. if the endangered or highly stressed areas of the cast body are subjected during the solidification to a cooling additional to the cooling received by other areas of the body. The behavior of alloys free of manganesc shows in cylinder heads to 50% of the durability achieved tn cylinder heads made of alloys containing manganese.

FIG. 2 shows the range of preferred alloy compositions wherein only I to 3% free magnesium (not bound to silicon) is present.

Further illustrative of the invention are the following Examples:

EXAMPLE 1 l ndcr heads of the type illustrated by air-cooled cylinder head l0 in FIG. 3 from an alloy poor in manganese. having the composition 5 2% Mg 1 (Vi Si 0.004% Bt. balance Al and customary contaminants. were subjected to an alternating thermal stress investigation after cooling the permanent mold with about 700 cm H O in the area of the spherical cap 11. The cooling was carried out by flowing the water through a metal mold core abutting against the spherical cap II and having cylinder inserts protruding into the inlet channel [2 and the outlet channel 13. The cooling effect pro vided by the cylinder inserts provides an additionally improved microstructure in the web 14. which is the most highly stressed portion of the head. The alternating load number was approximately 450 for the start of cracking of the web area between the inlet and outlet channels. Additionally in FIG. 3. axes l5. l6 and 17 are axes of cylindrical symmetry for. respectively. the inlet channel [2. the spherical cap I1. and the outlet channcl l3.

EXAMPLE 2 Cylinder heads of the same alloy as in Example l showed. after being cooled with 3.5 liters H 0 in the same area. an alternating load number of 750.

EX AM PLE 3 Cylinder heads of the manganese rich alloy w th the composition L01 Si 0.0049? Be balance Al and customary contaminants. were sub jccted. after cooling as in Example 2. to an alternating thermal stress. test and -iclded an alternating load numher of LS 0 to crackthrough.

Claims (9)

1. A HIGH-STRENGTH MANGANESE-CONTAINING AL-MG-SI ALLOY HAVING A FREE MAGNESIUM CONTENT OF 1.5 TO 4%, SAID ALLOY CONSISTING ESSENTIALLY OF 0.6 TO 1.8% MANGANESE, 2 TO 7% MAGNESIUM, 0.6 TO 2.5% SILICON, 0.1 TO 0.3% TITANIUM, AND HAVING BEEN SUBJECTED TO ONE OF THE FOLLOWING STEPS (A) AND (B): A. A SOLUTION TREATMENT UP TO 565*C MAXIMUM, B. A CORRESPONDING SOLUTION TREATMENT WITH SUBSEQUENT AGE-HARDENING AT TEMPERATURES NOT EXCEEDING THE HARDNESS MAXIMUM.

2. An alloy as claimed in claim 1, said alloy containing up to 1.5% Ni, up to 3% Cu, up to 0.1% beryllium, and at most 0.6% Fe.

3. An alloy as claimed in claim 1, said alloy containing manganese only in the quantities up to 1.2%, magnesium from 3.0 to 4.5%, silicon from 0.8 to 1.2%, and copper from 0.2 to 1.0%.

4. An alloy as claimed in claim 1, the magnesium content of said alloy being from 4.5 to 7.5% and the silicon content of said alloy being 0.8 to 2.5%.

5. An aluminum-magnesium-silicon alloy consisting essentially of 0.6 to 4.5% silicon, 2.5 to 11% magnesium, and aluminum, wherein the improvement comprises 1 to 4.5% free magnesium and at least one material selected from the group consisting of manganese at 0.6 to 1.8%, cobalt, chromium, vanadium, and molybdenum, where the sum of the gram-atoms of manganese, cobalt, vanadium, and molybdenum lies in the gram-atom range equivalent to 0.6 to 1.8% manganese.

6. An alloy as claimed in claim 5, said alloy containing at least one element selected from the group consisting of cobalt at at least 0.1% and chromium at at least 0.6%.

7. An alloy as claimed in claim 5, said alloy containing up to 1.5% Ni, up to 0.5% Cu, and at most 0.6% Fe.

8. An alloy as claimed in claim 5, said alloy containing 3% free magnesium.

9. An alloy as claimed in claim 5, said alloy containing at least one element selected from the group consisting of vanadium at at least 0.1% and molybdenum at at least 0.1%.

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