Heat resistant Al die cast material

Details Heat resistant Al die cast material Heat resistant Al die cast material

2002-03-27

2004-03-16

Wyszomierski, George (Department: 1742)

Alloys or metallic compositions

Aluminum base

Copper containing

C420S534000, C420S535000, C148S417000

Reexamination Certificate

active

06706242

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a heat resistant Al die cast material and, more particularly, to a heat resistant Al die cast material suited as a part of an internal combustion system, such as a piston.
BACKGROUND OF THE INVENTION
Conventional heat resistant Al materials consist of elements like Si, Cu, Mg, Ni and Ti added to Al at concentration levels appropriate for abrasion resistance, seizure resistance, and thermal resistance. An important application for heat resistant Al materials is pistons, which are a part of internal combustion systems. “Al alloy cast metal” is standardized in JIS H 5202 (1992). Table 1 in this standard lists the types of alloys and their codes, Table 2 lists chemical compositions, and Table 3 lists mechanical properties of cast metal test samples. Table 1 through Table 3 below summarize the JIS Table 1 through Table 3.
TABLE 1
Comments
Types of
Alloy
Codes
Types of Alloy
Mold
Characteristics
Applications
AC8A
Al-Si-Cu-Ni-Mg
metal mold
temperature
automotive
and abrasion
diesel engine
resistant
piston
small coeffi-
naval piston
cient of
pulley
expansion
bearings
high tensile
strength
AC8B
Al-Si-Cu-Ni-Mg
metal mold
same as above
automotive
piston
pulley
bearings
AC8C
Al-Si-Cu-Ni-Mg
metal mold
same as above
automotive
piston
pulley
bearings
As shown in the right-hand column in Table 1, under the “Applications” header, the AC8A, AC8B and AC8C Al alloy die cast metals are used for pistons in automobiles.
“Metal molds” listed under the “Type of Mold” in the third column of Table 1 represent regular metal casting.
TABLE 2
Unit: %
Chemical Compositions
Codes
Cu
Si
Mg
Zn
Fe
Mn
Ni
Ti
Pb
Sn
Cr
Al
AC8A
0.8-1.3
11.0-13.0
 0.7-1.3
≦0.15
≦0.8
≦0.15
 0.8-1.5
≦0.20
≦0.05
≦0.05
≦0.10
Balance
AC8B
2.0-4.0
 8.5-10.5
0.50-1.5
≦0.50
≦1.0
≦0.50
0.10-1.0
≦0.20
≦0.10
≦0.10
≦0.10
Balance
AC8C
2.0-4.0
 8.5-10.5
0.50-1.5
≦0.50
≦1.0
≦0.50
≦0.50
≦0.20
≦0.10
≦0.10
≦0.10
Balance
Table 2 shows the chemical compositions of the AC8A, AC8B and AC8C Al alloy die cast materials. AC8A is an Al—Si—Cu—Ni—Mg alloy containing 0.8% to 1.3% Cu, 11.0% to 13.0% Si, 0.7% to 1.3% Mg, and 0.8% to 1.5% Ni. AC8B is an Al—Si—Cu—Ni—Mg alloy containing 2.0% to 4.0% Cu, 8.5% to 10.5% Si, 0.5% to 1.5% Mg, and 0.1% to 1.0% Ni. AC8C is an Al—Si—Cu—Ni—Mg alloy containing 2.0% to 4.0% Cu, 8.5% to 10.5% Si, 0.5% to 1.5% Mg and 0.5% to 1.5% Ni.
As shown in Table 2, Zn content is less than or equal to 0.15% in AC8A and less than or equal to 0.50% in AC8B and AB8C. “Less than or equal to” means that Zn content can be 0%. In other words, Zn content should not exceed the prescribed amount (0.15% or 0.5%).
TABLE 3
Reference
Brinell
Heat Treatment
Tensile Test
Hard-
Annealing
Solution Treatment
Solution Treatment
Tensile
ness
Tem-
Tem-
Tem-
Strength
Length-
HB (10/
perature
perature
perature
Types
Codes
N/mm
2
ening %
500)
° C.
Time h
° C.
Time h
° C.
Time h
As cast
AC8A-F
≧170
—
Appx. 85
—
—
—
—
—
—
Age hardening
AC8A-
≧190
—
Appx. 90
—
—
—
—
Appx.
Appx. 4
T5
200
Solution treat-
AC8A-
≧270
—
Appx.
—
—
Appx.
Appx. 4
Appx.
Appx. 10
ment + age
T6
110
510
170
hardening
As cast
AC8B-F
≧170
—
Appx. 85
—
—
—
—
—
—
Age hardening
AC8B-
≧180
—
Appx. 90
—
—
—
—
Appx
Appx. 4
T5
200
Solution treat-
AC8B-
≧270
—
Appx.
—
—
Appx.
Appx. 4
Appx.
Appx. 10
ment + age
T6
110
510
170
hardening
As cast
AC8C-F
≧170
—
Appx. 85
—
—
—
—
—
—
Age hardening
AC8C-
≧180
—
Appx. 90
—
—
—
—
Appx.
Appx. 4
T5
200
Solution treat-
AC8C-
≧270
—
Appx.
—
—
Appx.
Appx. 4
Appx.
Appx. 10
ment + age
T6
110
510
170
hardening
Table 3 lists the mechanical properties of die cast test samples and provides information on whether or not any treatment is applied, and, if so, what type of treatment. For example, the “F” suffix that comes after the AC8A, AC8B and AC8C codes indicates that the alloy has only gone through a casting process. A “T5” suffix indicates that the alloy has been age hardened. A “T6” suffix indicates that the alloy has been age hardened after a solution treatment. For example, the AC8C-T6 alloy in the lower-most row goes through a solution treatment for approximately four hours at approximately 510° C., followed by approximately 10 hours of age hardening at approximately 170° C. The third column on Table 3 lists the tensile strengths. Tensile strength is lower for “F” compared with “T5”, while tensile strength is higher for “T6” compared with “T5”. Therefore, “T5” or “T6” treatment may be used for enhancing strength. These treatments are also effective for improving the dimensional stability during annealing.
TABLE 4
JIS HS5302 Al Alloy Die Cast
Reference Table 1: Mechanical properties of
as-cast die cast test samples
Tensile Tests
Tensile Strength N/mm
2
Lengthening %
Standard
Average
Standard
Types
Codes
Average Value
Deviation
Value
Deviation
Type 10
ADC10
245
20
2.0
0.6
Type 12
ADC12
225
39
1.5
0.6
Table 4 is a Reference Table 1 found in JIS H 5302 (1990). ADC10 and ADC12 are both Al—Si—Cu alloys, which do not contain Mg. Their compositions are given in JIS H 5302 (1990) and will not be listed here. ADC10 and ADC12 are Al alloy die cast metals whose compositions are different from the AC8A, AC8B and AC8C metals discussed above.
ADC10, which is an as-cast metal, has a tensile strength of 245 N/mm
2
, as shown in the third column of Table 4. ADC10 has a different composition and a much greater tensile strength than the AC8A-F, AC8B-F and AC8C-F metals mentioned above, whose tensile strengths are greater than or equal to 170 N/mm
2
. ADC12 exhibits similar properties.
While regular cast metals are produced by gravity casting, die cast metals are manufactured by high pressure casting. High pressure casting results in a more dense casting structure, which also results in higher strength.
The inventors of this invention assumed that it would be possible to achieve a much higher strength by treating die cast metals, if “T5” age hardening on the AC8A alloy increases the tensile strength from 170 N/mm
2
, to 190 N/mm
2
, and “T6” solvent treatment, followed by age hardening, increases AC8A's tensile strength from 170 N/mm2 to 270 N/mm
2
.
The inventors first performed an experiment in which an AC8A die cast metal was manufactured and treated with T6 solution treatment, followed by age hardening.
The resulting AC8A-T6 metal was covered by blisters and unusable. It is believed that the alloy incorporates air and other gases during the casting process and remain in the die cast metal as bubbles. These bubbles expand under 510° C. of heat during solvent treatment and lifted the Al alloy, which was softened under high heat.
Annealing temperature for the T5 age hardening, on the other hand, is around 200° C. Nevertheless, even a die cast AC8A-T5 metal shows blistering to a lesser degree. This experiment has confirmed that the ADC compositions are made different from the AC compositions in the JIS in order to avoid this phenomenon.
SUMMARY OF THE INVENTION
The inventors of this invention, however, believed it would be possible to perform the T5 age hardening on die cast metals with AC compositions by modifying the AC compositions. As a result of various research projects, the inventors discovered compositions that would make the AC die cast metal amenable to the T5 treatment.
This invention provides heat resistant Al die cast material that contains 12.5% to 14.0% of Si, 3.0% to 4.5% of Cu, 1.4% to 2.0% of Mg, and 1.12% to 2.4% of Zn. This die cast material is age hardened after die casting.
Because the die cast material having the above composition is amenable to age hardening, the material offers a much higher mechanical strength and seizure resistance. When Zn content is less than 1.12%, the die cast metal is prone to anneal cracks. When Zn content is more than 2.4%, the material exhibits less toughness. Therefore, Zn content should preferably be 1.12% to 2.4%.
Appropriate amounts of Mg and Zn added to an Al—Si—Cu alloy has resulted in a die cast metal that is amenable to annealing. This ty

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