Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/10—Alloys based on aluminium with zinc as the next major constituent

Definitions

• the most commonly used group of alloys Al-Si 7 -Mg
• cast materials made of A356.0, the most commonly used Al-Si 7 -Mg alloy can reliably guarantee ultimate tensile strength of 290 MPa (42,060 psi), and tensile yield strength of 220 MPa (31,908 psi) with elongations of 8% or greater.
• a variety of alternate alloys exist and are registered that exhibit higher strength than the Al-Si 7 -Mg alloys. However, these exhibit problems in castability, corrosion potential or fluidity that are not readily overcome. The alternate alloys are therefore less suitable for use.
• the alloy of the present invention is an Al-Zn-Mg base alloy for low pressure permanent or semi-permanent mold, squeeze, high pressure die, pressure or gravity casting, lost foam, investment casting, N-mold, or sand mold casting with the following composition ranges (all in weight percent): Zn: about 3.5-5.5%, Mg: about 1-3%, Cu: about 0.05-0.5%, Si: less than about 1.0%, Fe and other incidental impurities: less than about 0.30%, Mn: less than about 0.30%. [0008] Silicon up to about 1.0% may be employed to improve castability. Lower levels of silicon may be employed to increase strength. For some applications, manganese up to about 0.3%) may be employed to improve castability.
• the alloy may also contain grain refiners such as titanium diboride, TiB 2 or titanium carbide, TiC and/or anti-recrystallization agents such as zirconium or scandium. If titanium diboride is employed as a grain refiner, the concentration of boron in the alloy may be in a range from 0.0025% to 0.05%. Likewise, if titanium carbide is employed as a grain refiner, the concentration of carbon in the alloy may be in the range from 0.0025% to 0.05%. Typical grain refiners are aluminum alloys containing TiC or TiB 2 .
• Zirconium if used to prevent grain growth during solution heat treatment, is generally employed in a range below 0.2%. Scandium may also be used in a range below 0.3%.
• the alloy demonstrated 50%o higher tensile yield strength than is obtainable from A356.0-T6, while maintaining similar elongations. This will allow part designs requiring higher strength than alloys which are readily available today in Al-Si-Mg alloys such as A356.0-T6 or A357.0-T6. Fatigue performance in the T6 temper is increased over the A356.0-T6 material by 30%.
• the present invention is an aluminum alloy including from about 3.5-5.5% Zn, from about l-3%Mg, about 0.05-0.5% Cu and it contains less than about 1% Si.
• the present invention is a heat treatable shaped casting of an aluminum alloy including from about 3.5-5.5% Zn, from about 1-3% Mg, from about 0.05- 0.5%) Cu, and less than aboutl% Si.
• the present invention is a method of preparing a heat treatable aluminum alloy shaped casting.
• the method includes preparing a molten mass of an aluminum alloy including from about 3.5-5.5% Zn, from about 1-3% Mg, from about 0.05- 0.5%) Cu, and less than about 1% Si.
• the method further includes casting at least a portion of the molten mass in a mold configured to produce the shaped casting, permitting the molten mass to solidify, and removing the shaped casting from the mold.
• Figure 1 is a photograph of a cut surface of a cut sample of prior art A356.0 alloy cast in a shrinkage mold showing the shrinkage cracking tendency of the prior art A356.0 alloy
• Figure 2 is a photograph, similar to Figure 1, of a cut surface of a second sample of prior art A356.0 cast in a shrinkage mold showing the shrinkage cracking tendency of the prior art A356.0 alloy
• Figure 3 is a photograph of a cut surface of a sample of the alloy of the present invention cast in a shrinkage mold showing a lack of shrinkage cracking
• Figure 4 is a photograph, similar to Figure 3, of a cut surface of a second sample of the alloy of the present invention cast in a shrinkage mold showing a lack of shrinkage cracking
• Figure 5 presents strength and elongation data for directionally solidified samples of the present invention in T6 condition
• Figure 6 is a photograph of a front knuckle casting of an alloy according
• Table II presents room temperature mechanical properties of the directionally solidified alloys having the compositions shown in the first and third data lines of Table I.
• the first data line in Table II is for a directionally solidified casting comprised of the alloy of the first data line in Table I after five weeks of natural ageing.
• the second data line in Table 2 is for the same alloy after T5 heat treatment, and the third data line is for that alloy after T6 heat treatment.
• the fourth and fifth data lines in Table II are for the alloy in the bottom line of Table 1, which is a high copper alloy. This alloy, also, was subjected to a T6 heat treatment.
• Table III presents data for front knuckle castings as shown in Fig. 6. This is an alloy according to the present invention, and has the composition presented in the second data row in Table 1. The locations of tensile test samples 1, 2 and 3 are indicated in Fig. 6. Tests were performed on one casting subjected to a T5 heat treatment consisting of 160 °C for 6 hours, and one casting subjected to a T6 heat treatment consisting of solution heat treatment at 554 °C for 8 hours followed by a cold water quench, then by artificial ageing at 121 °C for 6 hours and 160 °C for 6 hours. Table HI: CS front knuckle room temperature mechanical properties
• Figure 9 is a graph showing staircase fatigue testing of the alloy of the present invention in T6 condition compared to the response of the prior art alloy, A356.0-T6 with a calculated mean value for A356.0-T6.
• the composition of the alloy of the present invention was as presented in the second data row of Table 1.
• the samples were solution heat treated at 526 °C or 554 °C, quenched and artificially aged at 160 °C for 6 hours. As seen earlier, the fatigue response of these samples is appreciably improved when compared to A356.0-T6 material.
• the mean fatigue strength of the alloy of the present invention was 109.33 MPa with a standard deviation of 9.02 MPa. The standard deviation of the mean fatigue strength was 3.01 MPa.
• the calculated mean fatigue strength at 10 7 cycles of A356.0 T6 is 70MPa.
• Corrosion resistance of the alloy of the present invention was tested using the ASTM Gl 10 corrosion test, which is the "Standard Practice for Evaluating Intergranular Corrosion Resistance of Heat Treatable Aluminum Alloys by Immersion in Sodium Chloride + Hydrogen Peroxide Solution".
• ASTM Gl 10 corrosion test which is the "Standard Practice for Evaluating Intergranular Corrosion Resistance of Heat Treatable Aluminum Alloys by Immersion in Sodium Chloride + Hydrogen Peroxide Solution”.
• specimens are immersed in a solution that contains 57g/L NaCl and 10 mL L H 2 O 2 (30%) for 6-24 hours. The specimens are then cross-sectioned and examined under optical microscope for type (intergranular corrosion or pitting) and depth of corrosion attack.
• Figure 10 is a graph presenting the depth of attack following the ASTM Gl 10 corrosion test after 6 hours and 24 hours for an alloy according to the present invention and for the alloy A356.0.
• Figures 11 and 12 are photomicrographs of an alloy according to the present invention after 24 hours exposure to the ASTM Gl 10 corrosion test. Nery little intergranular corrosion can be seen in these photomicrographs.
• Figure 13 is a photomicrograph of the A356.0 alloy after 24 hours of exposure to the ASTM Gl 10 corrosion test. Considerable intergranular corrosion can be seen in this photomicrograph.
• Table V presents the test results for the alloy compositions presented in Table IN.
• Table V ASTM G44 test of alloys with various Mg and Cu contents
• Figure 14 is a graph presenting the results of these tests. It is seen that, for alloys of the present invention, and at these high magnesium levels, increasing copper provides increased resistance to stress corrosion cracking.
• Figure 15 is a graph showing the effect of copper and magnesium levels on stress corrosion cracking for alloys of the present invention. This shows that for alloys according to the present invention which have magnesium in the range from 1.5-2%, it is desirable to include copper in the range from 0.25-0.3%.
• Table VI and VH present the results of plant trials in which repeated shots were made from a single liquid metal reservoir. One trial was performed on April 4; one was performed on June 4 and one on September 4. On each day, the composition for all the castings made varied very little.
• Table VI presents the ranges of the compositions of samples taken on each of the test days. The compositions contained high levels of magnesium and copper, which were expected to provide exceptionally high strength levels.
• Table VII presents the stress data, ultimate tensile strength, tensile yield strength, and elongation for four different locations in each casting.
• the column for sample numbers labels the individual castings.
• the column for location defines individual mechanical test samples cut from the castings.

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• Chemical & Material Sciences (AREA)
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• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Continuous Casting (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Body Structure For Vehicles (AREA)

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• 2005
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