US2018320259A1PendingUtilityA1
Method of increasing tensile strength of aluminum castings
Assignee: GM GLOBAL TECH OPERATIONS LLCPriority: May 2, 2017Filed: May 2, 2017Published: Nov 8, 2018
Est. expiryMay 2, 2037(~10.8 yrs left)· nominal 20-yr term from priority
C22F 1/002C22C 21/00C22F 1/04
45
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Claims
Abstract
A multiple step method increases net tensile strengths of high pressure die cast (HPDC) aluminum components through an alloy- and process-dependent thermal treatment. The highest temperature feasible for solution treatment of an HPDC casting is determined by computational thermodynamics, kinetics and the gas laws based on the alloy composition and gas pressure in the finally solidified parts. Determining the maximum solution temperature involves mapping pressure in the bubbles of solidified material to avoid the formation of blisters by surface adjacent bubbles in the casting. To reduce residual tensile stress, the HPDC parts are air cooled after the solution treatment. Finally, a specific, multiple temperature aging cycle is utilized to improve the aging response of air cooled HPDC parts and increase net tensile strength.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1 . A method of improving net tensile strength of high pressure die cast aluminum alloy part, comprising the steps of:
determining a highest temperature and a shortest time for solution treatment of a die cast aluminum alloy part by mapping pressure in bubbles of solidified aluminum alloy and utilizing pressure and volume gas laws, subjecting the die cast aluminum alloy part to solution treatment for the determined highest temperature and shortest time, air cooling the die cast aluminum alloy part to reduce residual tensile stress, and subjecting the die cast aluminum alloy part to a non-isothermal, multiple step aging cycle to improve net tensile strength.
2 . The method of claim 1 further including the step of determining a solidus temperature for the aluminum alloy die cast part.
3 . The method of claim 1 wherein the temperature and time of the solution treatment avoid blister formation.
4 . The method of claim 1 wherein the solution treatment time is below a time at which entrained gas bubbles will grow.
5 . The method of claim 1 wherein the mapping of pressure in bubbles utilizes the equation:
P
solidus
V
solidus
T
solidus
=
P
RT
V
RT
T
RT
=
σ
ys
@
ST
V
ST
T
ST
.
6 . The method of claim 1 wherein the solution treatment time determination utilizes the equations:
∂
C
∂
t
=
F
∂
2
C
∂
x
2
D
=
D
0
exp
(
-
Q
d
RT
)
where C is the alloy element content (at % or wt %), t is the time (seconds), x is the distance (meters); D is the diffusion coefficient (m̂2ŝ−1), D 0 is the diffusion constant (m̂2ŝ−1), R is universal gas constant (J/(mol. ° K)); T is the temperature (° K); and Q d is the activation energy (J/mol).
7 . The method of claim 1 wherein determining the non-isothermal, multiple step aging process utilizes the equations:
{
Min
(
T
,
t
)
∈
Ω
E
(
T
,
t
)
=
Min
(
T
,
t
)
∈
Ω
∮
T
(
t
)
dt
Max
(
T
,
t
)
∈
Ω
Δσ
ppt
(
T
,
t
,
C
)
Ω
=
{
0
<
T
<
T
c
;
0
<
t
<
∞
;
0
<
C
<
C
0
}
Δσ
ppt
(
T
,
t
,
C
)
≥
Δσ
target
where E(T,t) is the energy input, which is the function of temperature (T) and time (t), Δσ ppt (T, t,C) is the increase of material strength due to precipitate hardening, Δσ target is the desired strength increase needed for air-quench aluminum casting, C 0 and C are initial and current content (at % or wt %) of a hardening alloy element in an aluminum matrix during the aging cycle and Tc is the critical upper limit of aging temperature (° K).
8 . A method of improving net tensile strength of a high pressure die cast metal alloy component, comprising the steps of:
determining a highest temperature and a shortest time for solution treatment of a high pressure die cast component by mapping pressure in bubbles in the solidified, die cast component and utilizing computational thermodynamic properties and gas law equations, subjecting the die cast component to solution treatment for the determined highest temperature and time, air cooling the die cast component to reduce residual tensile stress, and subjecting the die cast component to a non-isothermal, multiple temperature aging process to improve its net tensile strength.
9 . The method of claim 8 further including the step of determining a solidus temperature for the die cast metal alloy component.
10 . The method of claim 8 wherein the temperature and time of the solution treatment avoid formation of blisters on a surface of the die cast metal alloy component.
11 . The method of claim 8 wherein the solution treatment time is shorter than a time at which entrained gas bubbles will grow
12 . The method of claim 8 wherein the mapping of pressure in bubbles utilizes the gas law equations:
P
solidus
V
solidus
T
solidus
=
P
RT
V
RT
T
RT
=
σ
ys
@
ST
V
ST
T
ST
.
13 . The method of claim 8 wherein the solution treatment time determination utilizes the equations:
∂
C
∂
t
=
F
∂
2
C
∂
x
2
D
=
D
0
exp
(
-
Q
d
RT
)
where C is the alloy element content (at % or wt %), t is the time (seconds), x is the distance (meters); D is the diffusion coefficient (m̂2ŝ−1), D 0 is the diffusion constant (m̂2ŝ−1), R is universal gas constant (J/(mol. ° K)); T is the temperature (° K); and Q d is the activation energy (J/mol).
14 . The method of claim 8 wherein determining the non-isothermal, multiple step aging process utilizes the equations:
{
Min
(
T
,
t
)
∈
Ω
E
(
T
,
t
)
=
Min
(
T
,
t
)
∈
Ω
∮
T
(
t
)
dt
Max
(
T
,
t
)
∈
Ω
Δσ
ppt
(
T
,
t
,
C
)
Ω
=
{
0
<
T
<
T
c
;
0
<
t
<
∞
;
0
<
C
<
C
0
}
Δσ
ppt
(
T
,
t
,
C
)
≥
Δσ
target
where E(T,t) is the energy input, which is the function of temperature (T) and time (t), Δσ ppt (T, t,C) is the increase of material strength due to precipitate hardening, Δσ target is the desired strength increase needed for air-quench aluminum casting, C 0 and C are initial and current content (at % or wt %) of a hardening alloy element in an aluminum matrix during the aging cycle and Tc is the critical upper limit of aging temperature (° K).
15 . A method of improving net tensile strength of a high pressure die cast aluminum alloy component, comprising the steps of:
determining a highest temperature and a shortest time for solution treatment of a high pressure die cast aluminum alloy component by mapping pressure in bubbles in the solidified, aluminum alloy die cast component and utilizing computational thermodynamics and gas laws, subjecting the die cast aluminum alloy component to a solution treatment for the determined highest temperature and time, subjecting the die cast aluminum alloy component to air cooling to reduce residual tensile stress, and subjecting the aluminum alloy component to a non-isothermal, multiple temperature aging cycle to improve net tensile strength.
16 . The method of claim 15 wherein said a high pressure die cast aluminum alloy component is an engine block.
17 . The method of claim 15 further including the step of determining a solidus temperature for the aluminum alloy.
18 . The method of claim 15 wherein the temperature and time of the solution treatment avoid formation of blisters.
19 . The method of claim 15 wherein the multiple temperature aging cycle utilizes at least a first, higher temperature and a second, lower temperature.Cited by (0)
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