Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1993-04-16
1994-06-21
Zimmerman, John
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
428650, 148535, 148537, B32B 1520, C22F 104
Patent
active
053227417
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to aluminum alloy sheets for primary use as automotive body panels and more particularly, to aluminum sheets or aluminum alloy sheets with improved press formability, especially bake hardenable, surface treated aluminum sheets or aluminum alloy sheets with improved press formability and a method for producing the same, and aluminum sheets or aluminum alloy sheets with improved press formability and corrosion resistance. Hereinafter, aluminum sheets and aluminum alloy sheets are generally designated aluminum alloy sheets.
PRIOR ART
From the standpoints of energy saving and the influence of carbon dioxide on the global environment, active efforts have been made for reducing the weight of automobiles. Among others, aluminum and aluminum alloys are highlighted for their advantages of material weight reductions and recycling and their use is increasing in these years.
However, aluminum alloy sheets have different properties from widely used conventional steel sheets and encounter many problems in applying them to automotive bodies. A typical problem is press forming. SPCC sheets as a typical steel sheet have an elongation of 45%, an r value of 1.4 and a limiting drawing ratio (LDR) as high as 2.15 whereas aluminum alloy sheets, for example, JIS A5182 sheets have only an elongation of 30%, an r value of 0.7 and a LDR as low as 1.8. Moreover aluminum alloy sheets of the bake hardenable type that heating for paint baking after press forming adds to strength are lower in formability as exemplified by JIS A6009-T4 sheets having an elongation of 25%, an r value of 0.7 and a LDR of 1.9. Since aluminum alloy sheets are very poor in formability, their application to automotive bodies is substantially restricted.
More specifically, actual application of aluminum alloy sheets to body panels was limited to light-forming members like hoods and their application to complex, heavy-forming members was difficult.
Since aluminum alloys were applied quite recently to automotive and analogous parts to be produced on a mass scale by press forming, no proposals or adequate means for solving the above-mentioned problems are available at present. The current manufacture is thus on progress with these problems unsolved. As a result, efforts to accomplish the social demand for automotive body weight reduction encounter difficulty. Investigating the press formability of aluminum alloy sheets, we found the fact that aluminum alloy sheets are significantly inferior in press formability to conventional cold rolled steel sheets because aluminum alloy sheets are not only poor in formability by themselves, but also experience greater sliding friction between their surface and the die used in press forming than the cold rolled steel sheets.
With the increased sliding friction, those portions of aluminum alloy sheets subject to severe sliding motion, for example, at beads of press dies for holding aluminum alloy sheets during press forming are prevented from smoothly entering the beads and can be ruptured in extreme cases. A comparison of optimum cushion pressure during press forming (the range of cushion pressure within which aluminum alloy sheets are not wrinkled or ruptured) between aluminum alloy sheets and cold rolled steel sheets reveals that aluminum alloy sheets have a significantly narrower range of optimum cushion pressure than cold rolled steel sheets so that the productivity of aluminum alloy sheets is low. It is thus strongly desired to improve the sliding frictional properties of aluminum alloy sheets.
It is believed that aluminum alloy sheets have poor sliding frictional properties because aluminum and aluminum alloys have a low melting point and high affinity to other metals, especially cast iron commonly used in press dies so that they are likely to stick to the dies.
Since sliding frictional properties upon press forming are largely affected by the physical properties of aluminum alloy sheets on the surface in direct contact with dies, it was attempted to improve sliding frictio
REFERENCES:
patent: 2676916 (1954-04-01), Zelley
patent: 3055087 (1962-09-01), Fink
patent: 3551122 (1970-12-01), Gulla
Copy of European Search Report (6 pages), Jul. 28, 1993, for EP 92 91 6223.
Hashiguchi Koichi
Hira Takaaki
Imanaka Makoto
Matsumoto Yoshihiro
Morito Nobuyuki
Furukawa Aluminum Co.
Kawasaki Steel Corporation
Toyota Motor Corporation
Zimmerman John
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