Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1995-11-22
1997-11-25
Simmons, David A.
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148694, 148698, 148699, 148701, C22F 105, C22F 1057
Patent
active
056907583
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fabrication process to improve the mechanical and forming properties of aluminum alloy sheet, used particularly in automotive bodies.
2. Description of the Prior Art
Automotive bodies are traditionally made from cold-rolled steel sheet.
In the past few years, auto manufacturers have attempted to reduce the weight of their models by studying the possibility of using aluminum alloy of the Al-Mg-Si type in producing automotive bodies, among other parts.
In this technology, the Al-Mg-Si alloy sheet is formed into an element of an auto body after solution treatment followed by natural aging into the T4 state. After forming, a hardening step through aging ("bake hardening" heat treatment) applied during the application or curing of the paints, imparts to the body the required properties.
The main difficulty raised by the use of aluminum alloys in automotive bodies is their insufficient formability. The formability of aluminum alloys, and in particular that of Al-Mg-Si alloys, therefore needs to be greatly improved.
Furthermore, aluminum alloy sheet suffers from low mechanical properties compared to steel sheet. Manufacturers are therefore interested in curing processes that, on the one hand, are efficient enough to impart to those sheets high mechanical properties and, on the other hand, that require fairly short treatment times and low temperatures to minimize processing costs.
SUMMARY OF THE INVENTION
The present invention relates to a process for the fabrication of aluminum alloy sheet having high formability, characterized in that an aluminum alloy sheet composed of 0.3 to 1.7% (by weight) Si, 0.01 to 1.2% Cu, 0.01 to 1.1% Mn, 0.4 to 1.4% Mg, less than 1.0% Fe and, the remainder, Al along with the inescapable impurities, is subjected to a continuous solution treatment for at least 3 seconds above 450.degree. C., followed by cooling between 60.degree. and 250.degree. C. and a preaging process for 1 minute to 10 hours at the previous cooling temperature of between 60.degree. and 250.degree. C.
The alloy may contain one or more elements, selected from among Cr (between 0.04 and 0.4%), Zn (less than 0.25%), Zr (less than 0.4%) and Ti (less than 0.2%).
The ranges of composition imposed in the invention on the different alloying elements are justified by the following: Si improves the mechanical properties by forming an Mg.sub.2 Si precipitate with Mg during the curing of the paint.
Its composition is selected in the 0.3-1.7% range by weight. Indeed, below 0.3% its effect is insufficient and above 1.7%, its formability after solution treatment decreases.
Mg improves the formability by forming a solid solution in the matrix after the solution treatment. Furthermore, it improves the mechanical properties by forming an Mg.sub.2 Si precipitate with Si during the curing of the paint. Its composition is selected in the 0.4-1.4% range by weight. Indeed, below 0.4%, the increase in mechanical properties is not sufficient and above 1.4%, the formability after the solution treatment decreases.
Cu improves the mechanical properties by precipitating in particular the q' and S phases as well as GP (Guinier-Preston) zones, during the curing of the paint. Its composition is selected in the 0.01-1.2% range by weight. Indeed, below 0.01%, the increase in mechanical properties is not sufficient and above 1.2%, the corrosion resistance decreases.
Mn and Cr refine the grain size and the mechanical properties of the matrix. Their composition is selected in the 0.01-1.1% and the 0.04-0.4% range by weight, respectively. Indeed, at lower concentrations, their effect is insufficient and above the upper range, the formability after the solution treatment decreases.
Zn improves the mechanical properties. Zr and Ti refine the microstructure. Their composition is selected to be lower than 0.25%, 0.4% and 0.2% respectively. Above these values, the formability will be too low.
Fe, a general impurity in aluminum, must be kept below 1.0% by weight. Above
REFERENCES:
patent: 3135633 (1964-06-01), Hornus
patent: 5098490 (1992-03-01), Huu
patent: 5582660 (1996-12-01), Erickson et al.
Singleton, Jr., "Quench-Aging Makes Headway With 6061 Aluminum", The Iron Age, vol. 192, No. 24, Dec. 12, 1963, pp. 94,95.
Kishino Kunihiko
Oh Binrun
Suzuki Yuichi
Elve M. Alexandra
Kaiser Aluminum & Chemical Corporation
McGarrigle Philip L.
Simmons David A.
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