Effects of HPT on microstructure and mechanical properties of extruded secondary Al 6061 alloy.

Abstract

The influence of high pressure-torsion (HPT) on the microstructure and mechanical properties of extruded secondary aluminum 6061 alloy was investigated. Although previous HPT-processed materials have mainly been derived from primary wrought alloys, the novelty of the current study was derived from integrating HPT into the processing of secondary recycled wrought alloys. Mixed wrought aluminum scrap was hand-sorted to obtain a secondary aluminum with composition similar to Al 6061 wrought alloy. The resulting samples were extruded using a customised general-purpose pneumatic press. The extruded rods have a diameter of 14 mm. Discs with 10 mm diameter and 1.2 mm thickness were machined from the extruded rods and were further ground and polished to reduce disc thickness to 0.8 mm. The discs were then processed by HPT at 0.25, 0.5, 1, 2, 5 and 10 turns with 6.0 GPa constant pressure. Optical microscopy, SEM and EDS analysis, microhardness and tensile tests were conducted on the as-cast, as-extruded and HPT-processed disc samples. The results showed that HPT processing refined the grain size and increased microhardness from 50 to 110 HV. Tensile test results demonstrated that HPT samples processed to 10 turns had UTS value of 381 MPa while non-HPT processed samples (as-cast and as-extruded) had UTS values of 84 and 214 MPa. These property improvements for secondary Al 6061 alloy opens up potential applications such as in micro-electro-mechanical systems.