Effect of Heat Treatment on Forming Limit Strains in Aluminium Alloy Sheets

This paper focuses on formability value of aluminium alloy sheet in the stretch forming operation. The formability of materials can be varied with respect to different heat treatment processes. Aluminium alloy sheets were prepared for the required size under cold rolled, polymer quenched and annealed conditions. A hemispherical punch and ring die were designed and fabricated for performing the stretch forming operations. The surface of each aluminium alloy sheet was imprinted with circular grid pattern of diameter 5 mm and these sheets were stretch formed by using the punch and die. The change in grid pattern after deformation were measured and analysed for major and minor strain values. From these values a formability limit diagram was constructed for each heat treatment conditions. From the forming limit diagram it is found that the annealed and polymer quenched aluminium alloy sheets have good formability. For increasing the formability value of the Aluminium alloy sheets, the stretch forming of the annealed specimen was repeated by applying the proper lubricant (SAE 40) in between the work and punch surface. It is found 2% increase in major strain in lubricating condition. The tensile strength of the sheet metal is found in UTM with constant cross head speed. The tensile strength of polymer quenched aluminium alloy sheet is placed very close to the cold rolled one. Hence polymer quenched aluminium sheets are recommended for making automobile components.