KR20070004987A - Heat treatable al-zn-mg-cu alloy for aerospace and automotive castings - Google Patents

Abstract

A heat treatable aluminum alloy for shaped castings includes from about 3.5-5.5% Zn, from about 1-3% Mg, about 0.05-0.5% Cu, and less than about 1% Si. ® KIPO & WIPO 2007

Description

Heat Treatable AL-ZN-MG-CU ALLOY FOR AEROSPACE AND AUTOMOTIVE CASTINGS}

Cross Reference with Related Application

This application claims the benefit of US Provisional Application Serial No. 60 / 564,813, filed April 22, 2004, which is incorporated herein by reference in its entirety. It is also closely related to the patent application "Heat-treatable Al-Zn-Mg alloy for aerospace and automotive castings" which is simultaneously filed with this application, which is also incorporated herein by reference.

Field of technology

The present invention is an aluminum alloy for aerospace and automotive molding castings, castings made of this alloy, and a method for producing casting components of this alloy.

Cast aluminum parts are used in structural applications to reduce weight in automotive suspensions. The most commonly used alloy soldier Al-Si ₇ -Mg has well established strength limits. To achieve lighter weight parts, higher strength materials are required, and material properties for the design must be established. Currently, the Al-Si ₇ -Mg alloy most commonly used as a casting material made of A356.0 can reliably guarantee a tensile strength of 290 MPa (42,060 psi) and a tensile yield strength of 220 MPa (31,908 psi), Elongation is 8% or more.

Various alternative alloys exist and are reported to exhibit higher strength than Al-Si ₇ -Mg alloys. However, they present problems with castability, corrosion potential or flowability, which cannot be easily overcome. Thus, alternative alloys are less suitable for use.

If high strength is required, forged products are often used. These are usually more expensive than cast products. If cast products can be used in place of forged products without loss of strength, elongation, corrosion resistance, fatigue strength, etc., there is a potential cost savings. This is true for both automotive and aerospace applications.

Cast alloys that exhibit higher tensile strength and fatigue resistance than Al-Si ₇ -Mg materials are preferred. Such improvements can be used to reduce weight in new or existing parts, and existing parts can be more advantageously redesigned using improved material properties.

Introduction of the invention

The alloy of the present invention is an Al-Zn-Mg based alloy having the following composition range (all wt%), which is a low pressure permanent or semi-permanent mold, squeeze, high pressure die, pressurized or gravity casting, lost foaming, investment casting, V-shaped mold, Or suitable for sand casting.

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%.

Silicon can be used up to about 1.0% to improve castability. Lower levels of silicon may be used to increase strength. In some applications, up to about 0.3% manganese may be used to improve castability. Manganese may not be used in other applications.

The alloy may also contain crystal refining agents such as titanium boride TiB ₂ or titanium carbide TiC and / or recrystallization inhibitors such as zirconium or scandium. When titanium boride is used as the crystal refiner, the concentration of boron in the alloy may range from 0.0025% to 0.05%. Likewise, when titanium carbide is used as the crystalline refiner, the concentration of carbon in the alloy may range from 0.0025% to 0.05%. Typical crystal refiners are aluminum alloys containing TiC or TiB ₂ .

If zirconium is used to prevent crystal growth during the solution treatment, zirconium is generally used in the range of 0.2% or less. In addition, scandium may be used in the range of 0.3% or less.

At T6 temper, the alloy showed 50% higher tensile yield strength than that obtained from A356.0-T6 while maintaining similar elongation. This will allow part designs that require higher strength than those currently readily available in Al-Si-Mg alloys such as A356.0-T6 or A357.0-T6. At T6 tempers, fatigue performance is increased by 30% compared to A356.0-T6 materials.

Summary of the Invention

In one embodiment, the present invention is an aluminum alloy comprising about 3.5-5.5% Zn, about 1-3% Mg, about 0.05-0.5% Cu, which contains less than about 1% Si.

In another aspect, the present invention is a heat treatable molding casting of an aluminum alloy comprising about 3.5-5.5% Zn, about 1-3% Mg, about 0.05-0.5% Cu, and less than about 1% Si.

In another aspect, the invention is a method of making a heat treatable aluminum alloy molding casting. The method includes preparing a molten mass of an aluminum alloy comprising about 3.5-5.5% Zn, about 1-3% Mg, 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 a molding casting, solidifying the molten mass, and removing the molding casting from the mold.

1 is a photograph of the cut surface of a cut sample of prior art A356.0 alloy cast in a shrink mold, showing the shrinkage cracking tendency of the prior art A356.0 alloy.

FIG. 2 is a photograph similar to FIG. 1 of the cut surface of a second sample of prior art A356.0 cast in a shrink mold, showing the shrinkage cracking tendency of prior art A356.0 alloy.

3 is a photograph of the cut surface of an alloy sample of the present invention cast in a shrink mold, showing no shrinkage cracks.

FIG. 4 is a photograph similar to FIG. 3 of the cut surface of the second sample of the alloy of the invention cast in a shrink mold, showing no shrinkage cracks.

5 shows the strength and elongation data for the directionally solidified samples of the present invention at T6 conditions.

6 is a photograph of a front knuckle casting of an alloy according to the present invention, showing where a tensile test sample was obtained.

FIG. 7 is a graph of strength and elongation data after T5 and T6 heat treatment for tensile test samples cut from the casting shown in FIG. 6.

8 is a graph showing the S-N fatigue reaction (ASTM E466 test, R = -1) of the alloy of the present invention at T6 condition compared to the reaction of prior art A356.0-T6.

FIG. 9 is a graph showing the step-by-step fatigue test of the alloy of the present invention at T6 conditions compared to the reaction of prior art A356.0-T6, with average fatigue strength for A356.0-T6.

10 is a graph showing the damage depth after the grain boundary corrosion test of the alloy of the present invention, compared to the prior art alloy A356.

11 is a photomicrograph of the casting surface of the sample after the grain boundary corrosion test of the alloy according to the present invention.

12 is a micrograph of the machined surface of the sample after the grain boundary corrosion test of the alloy according to the present invention.

13 is a micrograph after a grain boundary corrosion test of prior art alloy A356.

14 is a graph showing the results of a stress corrosion test for alloys of the present invention having various levels of copper.

15 is a graph showing the effect of copper and magnesium levels on stress corrosion cracking of alloys of the present invention.

Detailed Description of Preferred Embodiments and Comparison with Prior Art Alloys

When referring to any numerical range of values herein, it is understood that such range includes angles and all numbers and / or fractions between the minimum and maximum values of the stated range. For example, the range of about 3.5 to 5.5 wt% zinc clearly includes all intermediate values of about 3.6, 3.7, 3.8 and 3.9%, including 5.3, 5.35, 5.4, 5.475 and 5.499% Zn and below. It includes everything. The same applies to each of the other numerical properties and elemental ranges presented herein.

Table I shows the composition data of the alloys tested. The composition shown in the first and third lines is for a directionally solidified fetish. The second line is about the composition used in the molding casting. The molding casting was the front knuckle shown in FIG.

Table II shows the mechanical properties at room temperature of aromatically solidified alloys having the compositions shown in the first and third data lines of Table I. The first data line in Table II is the data after five weeks of natural aging of the directionally solidified casting made of the alloy of the first data line in Table I. The second data line in Table II is the data after T5 heat treatment of the same alloy, and the third data line is the data after T6 heat treatment of the alloy. The fourth and fifth data lines of Table II are for the alloy shown in the last row of Table I, which is a high copper alloy. This alloy was also subjected to T6 heat treatment.

The development of the mechanical properties during heat treatment of the directionally solidified sample of the present invention is shown in FIG. 5. The composition of these samples is shown in the first row of data in Table I. The solution treatment was performed for 8 hours at 1030 ° F. (554 ° C.), then quenched with cold water and then artificially aged. After varying amounts of artificial aging, the samples were removed from the oven and subjected to mechanical testing. Properties measured were TYS, UTS and elongation. The duration of artificial aging was 15 hours. The temperature was 250 ° F. (121 ° C.) for the first six hours. The temperature was 320 [deg.] F. (160 [deg.] C.) for the next nine hours. TYS and UTS values refer to the scale on the left, and elongation values refer to the scale on the right.

Table III shows the data for the front knuckle casting shown in FIG. 6. This is an alloy according to the invention and has the composition shown in the second data line of Table I. The locations of tensile test samples 1, 2 and 3 are shown in FIG. One casting was subjected to T5 heat treatment consisting of 160 ° C. and 6 hours, one casting was 554 ° C., 8 hours solution treatment followed by cold water quenching, followed by 121 ° C., 6 hours and 160 ° C., 6 hours artificial aging treatment. The test was carried out by performing a heat treatment.

In Table III, it is noted that extremely high tensile strength values and good elongation were obtained for the alloy at both T5 and T6 tempers. Also note that the composition was as shown in the second row of data in Table I. The data shown in Table III is shown graphically in Table 7.

The graph of FIG. 8 shows the S-N fatigue reaction of the alloy of the present invention in comparison with the reaction of prior art alloys A356.0-T6. This test was ASTM E466, R = -1. After 100,000 cycles, it can be seen that the alloy of the present invention is significantly superior to the alloys of the prior art.

9 is a graph showing the step-by-step fatigue test of the alloy of the present invention under the T6 condition compared with the reaction of the prior art alloy A356.0-T6, the average value for A356.0-T6 was calculated. The composition of the alloy of the present invention was as shown in the second data line of Table I.

Samples were solution treated at 526 ° C. or 554 ° C., then quenched and artificially aged at 160 ° C. for 6 hours. As already shown, the fatigue response of these samples is significantly improved compared to the A356.0-T6 material.

The average fatigue strength of the alloy of the present invention was 109.33 MPa, with a standard deviation of 0.02 MPa. The standard deviation of average fatigue strength was 3.01 MPa. The average fatigue strength calculated at 10 ⁷ cycles of A356.0-T6 is 70 MPa.

The corrosion resistance of the alloy of the present invention was tested using the ASTM G110 corrosion test, "Standard Practice for Evaluating the Grain Boundary Corrosion Resistance of Aluminum Alloys Heat Treatable by Soaking in Sodium Chloride + Hydrogen Peroxide Solution".

In this test, the samples are soaked for 6-24 hours in a solution containing 57 g / L NaCl and 10 mL / LH ₂ O ₂ (30%). Next, the sample is cut in cross section and tested under the optical microscope for the type (grain corrosion or corrosion) and depth of corrosion damage.

10 is a graph showing the damage depth according to the ASTM G110 corrosion test after 6 hours and 24 hours for the alloy and A356.0 alloy according to the present invention.

11 and 12 are micrographs of alloys according to the present invention after 24 hours exposure to ASTM G110 corrosion test. Very few grain boundary corrosion can be seen in these micrographs.

FIG. 13 is a micrograph of an A356.0 alloy after 24 hours exposure to ASTM G110 corrosion test. Significant grain boundary corrosion can be seen in this micrograph.

The corrosion test was also performed using the ASTM G44 test, "Standard Practice for Exposure to Metals and Alloys by Repeated Immersion in Neutral 3.5% Sodium Chloride Solution." In this test, a stressed sample was subjected to a 1-hour cycle comprising immersion in 3.5% NaCl solution for 10 minutes and then left in laboratory air for 50 minutes. Repeat this one-hour cycle. Samples are regularly inspected for cracks and breaks during the test.

Table IV shows the compositions of the various alloys according to the invention used in the ASTM G44 test.

Table V shows the test results for the alloy compositions shown in Table IV.

14 is a graph showing the results of these tests. For the alloy of the present invention, it can be seen that at high magnesium levels, an increase in copper increases the resistance to stress corrosion cracking.

15 is a graph showing the effect of copper and magnesium levels on stress corrosion cracking of alloys of the present invention. FIG. 15 shows that for the alloy according to the invention having magnesium in the range of 1.5 to 2%, it is preferable to include copper in the range of 0.25 to 0.3%.

Tables VI and VII show the results of a plant test where shots were repeatedly made from a single liquid metal reservoir. One test was conducted on April 4, one was tested on June 4, and one was tested on September 4. The composition for all castings at each date was very slightly different.

Table VI shows the composition ranges of the samples taken on each test day. The composition contained high levels of magnesium and copper, which was expected to provide unexpectedly high strength levels.

Table VII shows the stress data, final tensile strength, tensile yield strength, and elongation for four different locations in each casting. The sample number column represents each casting. The location column defines each mechanical test sample cut from the casting.

Note that at high levels of magnesium and copper, excellent strength levels are obtained with good elongation.

While the presently preferred embodiments of the invention have been presented above, it should be understood that the invention may be embodied in other ways within the scope of the appended claims.

Claims (27)

Zn: about 3.5 to 5.5% by weight as alloy component; Mg: about 1-3%; Cu: about 0.05-0.5%; Si: heat treatable aluminum alloy for molding castings comprising less than about 1%. The aluminum alloy of claim 1, further comprising at least one crystal refiner selected from the group consisting of boron, carbon, and combinations thereof. 3. The aluminum alloy of claim 2, wherein the at least one crystal refiner comprises boron in the range from about 0.0025% to about 0.05%. The aluminum alloy of claim 2, wherein the at least one crystal refiner comprises carbon in the range of about 0.0025% to about 0.05%. The aluminum alloy of claim 1, further comprising at least one anti-crystallization agent selected from the group consisting of zirconium, scandium, and combinations thereof. The aluminum alloy of claim 5, wherein the at least one anti-crystallization agent comprises zirconium in the range of 0.2% or less. 6. The aluminum alloy of claim 5, wherein said at least one anti-crystallization agent comprises scandium in the range of 0.3% or less. The aluminum alloy of claim 1, wherein the zinc is in a concentration of about 4.2% to 4.8%. The aluminum alloy of claim 1, wherein the magnesium is in a concentration of about 1.7% to 2.3%. 9. The aluminum alloy of claim 8, wherein the copper is at a concentration of about 0.25-0.3%. The aluminum alloy of claim 10, wherein the copper is in a concentration of about 0.27% to 0.28%. The aluminum alloy of claim 1, wherein the concentration of iron in the alloy is less than about 0.3%. The aluminum alloy of claim 1, wherein the concentration of manganese in the alloy is less than about 0.3%. Zn as alloy component: about 3.5 to 5.5%; Mg: about 1-3%; Cu: about 0.05-0.5%; Si: Molded casting of an aluminum alloy comprising less than about 1%. The molding casting according to claim 14 after T5 heat treatment. The molding casting according to claim 14 after T6 heat treatment. 15. The molding casting of claim 14 wherein the zinc is at a concentration of about 4.2-4.8%. 15. The molding casting of claim 14 wherein the magnesium is in a concentration of about 1.8-2.2%. 15. The molding casting of claim 14 wherein the copper is at a concentration of about 0.25-0.3%. 15. The molding casting of claim 14 wherein the copper is at a concentration of about 0.27% to 0.28%. Zn as alloy component: about 3.5 to 5.5%; Mg: about 1-3%; Cu: about 0.05-0.5%; Si: producing a molten mass of aluminum alloy comprising less than about 1%; Casting at least a portion of the molten mass in a mold configured to produce a molding casting; Solidifying the molten mass in the mold; And Removing a molding casting from the mold A manufacturing method of an aluminum alloy molding casting comprising a. 22. The method of claim 21, further comprising subjecting the molding casting to a T5 heat treatment. 22. The method of claim 21, further comprising subjecting the molding casting to a T6 heat treatment. 22. The method of claim 21, wherein the zinc is at a concentration of about 4.2-4.8%. 22. The method of claim 21, wherein the magnesium is at a concentration of about 1.8-2.2%. The method of claim 21 wherein the copper is at a concentration of about 0.25-0.3%. 27. The method of claim 26, wherein the copper is at a concentration of about 0.27% to 0.28%.

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