EFFECTS OF METALLURGICAL AND TRIBOLOGICAL FACTORS ON FORMABILITY LIMITS AND SURFACE CONDITION OF ALUMINUM 7075 SHEET PRODUCTS

A systematic investigation was carried out on the effects of metallurg ical and tribological factors on the formability and surface condition of 7075 aluminum sheet products. It included the effects of sheet thi ckness and type of temper on the formability limits. The free-flow for ming conditions were simulated by tensile testing. The important proce ss parameters in sheet forming operations were tested in stretch formi ng using a 40 mm diameter hemispherical punch. Three different interfa ce friction conditions were tested. The results showed that solution t reated alloy has the optimum sheet formability; however the alloy unde r this temper condition exhibits the undesirable serrated yielding phe nomenon. Improving lubricity and/or increasing sheet thickness will im prove the uniformity of deformation. Surface roughness increases as de formation increases for all tempers. Both the annealed and fully-harde ned alloys exhibit good surface finish in the free-flow zone. The anne aled 7075 alloy has a combination of reasonable formability and good s urface quality after deformation, but it requires two heat treatment o perations to regain the strength of a fully-hardened condition.