Data processing: measuring – calibrating – or testing – Measurement system – Temperature measuring system
Reexamination Certificate
1998-09-10
2001-07-31
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Temperature measuring system
C702S023000, C702S027000, C702S030000, C164S004100, C164S057100, C164S151400
Reexamination Certificate
active
06269321
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to aluminum castings, and, more particularly, to a method for predicting mechanical properties cast aluminum alloy structural components.
BACKGROUND OF THE INVENTION
Application of cast aluminum for engine structures has been increasing in recent years. These new applications include engine components for high power density and heavy duty service that were traditionally cast from gray iron. Individual aluminum alloy castings produced within a single production run can vary substantially in mechanical and physical properties. For example, tensile properties may vary between regions or locations in the same casting due to differences in local rates of solidification. Variations may also occur between castings due to slight changes within the acceptable limits for adding of the constituents to form the alloy and the latitudes of time and temperature of heat treatment and processing.
Historically, the tests conducted for determining the physical properties of a casting tended to destroy or weaken the casting. More recently, a testing method has been developed that is based on a relationship that correlates a microstructural parameter of a dendritic alloy sample to ductility. The method includes counting substantially all of the metal dendrite arms of the primary metal phase within a surface area of a selected location and correlating the number of metal dendrite arms per unit area to the ductility of the location. The number of dendrite arms is correlated to the ductility of the dendritic alloy by means of an equation:
EL
=
c
(
ANB
-
C
D
)
,
where
EL=total average elongation (ductility) in percent,
N=number of cells of the primary metal of the alloy counted per unit area, and
A, B, C, D=empirical constants.
Further effort has refined the ductility equation to account for porosity of the sample. The method includes selecting a surface area of the casting for determining ductility; determining the number of metal cells of the primary metal within the surface area of the casting; measuring the aspect ratio of the eutectic particles and the porosity within the surface area of the casting; and determining ductility of the casting by relating the number of cells of primary metal per unit area with the measured aspect ratio of the eutectic particles and the measured porosity according to the equation:
EL
=
10
{
[
C
1
(
N
0.5
)
-
C
2
(
N
0.5
AR
)
+
C
3
(
-
1
AR
)
-
C
4
(
P
0.5
)
-
C
5
-
c
]
(
k
+
b
)
}
where
EL is the total average elongation (ductility of casting in percent),
N is the number of cells of the primary metal of the casting per unit area,
C
1
(NO
0.5
) is the solidification rate,
C
1
(
N
0.5
AR
)
is the solidification rate (SR),
C
2
(
N
0.5
AR
)
is the SR and eutectic modification (EM) interaction; AR is the aspect ratio of the eutectic particles,
C
3
(
-
1
AR
)
is the EM from alloying and solution heat treatment,
C
4
(P
0.5
) is the porosity, percent coverage, ductility reduction,
C
5
is a coefficient characteristic of the chemistry of the alloy, and
c, k, and b are empirical constants for the alloy and
C
1
, C
2
, C
3
, and C
5
are coefficients from statistical multiple regression of the alloy.
While progress has been made, designing components for high power density, heavy duty automotive applications reveals a lack of detailed information on the metallurgy of solidification of the aluminum alloys sufficient to predict mechanical and physical properties. It is desirable to predict physical and mechanical properties before a casting is made.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a method for quantitatively predicting and consequently minimizing the amount of certain critical phases (e.g. eutectic Al
2
Cu) formed during solidification of Al—Si alloys used in a vehicle engine component or other structural component comprises developing a micromodel to simulate microstructure evolution in cast aluminum alloys, calibrating the micromodel using experimental thermal analysis cooling curves and an optimization process, simulating microstructure evolution and cooling curves in a casting using the calibrated micromodel, and predicting critical phase (e.g. Al
2
Cu) precipitation in the casting as a function of solidification conditions.
The micromodel simulates microstructure evolution in castings such as 319 and A356 aluminum alloys which are similar in composition but differ in copper content. The model is calibrated using experimental thermal analysis cooling curves and an optimization methodology. The model is then used to simulate microstructure evolution and cooling curves in a special wedge casting . The model is able to predict critical phases (e.g. Al
2
Cu) precipitation as a function of solidification conditions.
A basic finding for Al—Si—Cu alloys such as 319 Al is that at low cooling rates, a high degree of segregation of copper in liquid occurs which leads to a high amount of eutectic Al
2
Cu. This condition leads to reduced strength due to depletion of Cu in the primary Al dendrite and low amount of fine &thgr;″,&thgr;′ and &thgr; precipitates which form during heat treatment. At higher cooling rates the amount of copper available in liquid is less and a lower amount of eutectic Al
2
Cu is formed. This leads to higher strength due to optimum levels of Cu in the primary Al dendrites and high amounts of the fine &thgr;″,&thgr;′ and &thgr; precipitates which form during heat treatment. The model allows casting process variables to be varied with predictable results so that the casting process and resulting properties can be controlled via the micromodel.
This method can also be used to predict and control the influence of solidification conditions on formation of critical phases such as Al
6
(Fe,Mn)
3
Si and AlFe which result when present in Al—Si alloys.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.
REFERENCES:
patent: H633 (1989-06-01), McLellan
patent: 4381666 (1983-05-01), Feiertag et al.
patent: 4598754 (1986-07-01), Yen et al.
Allison John Edmond
Donlon William Thomas
Palle Nagendra
Vijayaraghavan Ravi
Zindel Jacob Wesley
Ford Global Technologies, Inc
May Roger L.
Porcari Damain
Shah Kamini
Vo Hien
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