Forming Performance of Aluminum Alloy Sheets for Automobile Body Panels

Improvement of material characteristic values, adjustment of forming conditions as well as introduction of new forming technics are necessary to promote wide application of aluminum alloy sheets into automotive parts. 5000 series and 6000 series aluminum alloy sheets are concerned about the relationship between material characteristic values and fundamental forming ability required to apply them to automobile body parts as well as the effect of lubricant on their formability.

The hardening parameters, n values, of them are larger than those of cold-rolled steel sheets. However, the r values and the local elongations are extremely small. The improvement of stretch formability owing to increase of n value is smaller than that of the steel sheets. Inferior deep drawability of the aluminum alloy sheets is due to low fracture resistance force caused by low r value. The utilization of a dry lubricant gives considerably lower coefficients of friction both in a flat sheet drawing test and in the draw bead test rather than typical liquid lubricants. The shape fix-ability of the aluminum alloy sheets is inferior to that of the steel sheets even if they have the same yield strength,as the steel sheets of their lower Young's modulus. In the case of the aluminum alloy sheets, the application of higher blank holding force and the utilization of a dry lubricant improve the shape fix-ability, and result in better panel stiffness.