Influence of Specimen Preparation Methods on the Mechanical Properties and Superplastic Behavior of AA5083 Sheets

Abstract

The process used to fabricate tensile specimens inevitably introduces imperfections at their edges, which can affect the resulting experimental mechanical properties. It has been reported that, for ambient temperature testing, tensile specimens prepared by less aggressive machining methods yield more accurate data due to the absence of plastic deformation at the edges. However, for superplastic forming (SPF) where forming is performed at elevated temperatures, the results are different. In this study, AA5083 sheet specimens were prepared using different machining methods: wire-electro-discharge machining, waterjet cutting, and conventional milling. Mechanical properties were determined from tensile tests carried out at 450 °C and at a quasi-static strain rate. The edges of tensile specimens were observed under optical and scanning electron microscopes (SEM) both before and after testing. It was found that milled specimens resulted in greater values of total elongation. The microscopic investigation revealed that specimens whose edges have a lower arithmetic mean roughness (Ra) have greater values of elongation. The SEM investigation also revealed that micro-cracks are more prevalent at the edges of specimens that have a greater surface roughness. Therefore, tensile specimens used to characterize sheet mechanical properties in view of SPF applications should be fabricated by a process that yields a lower surface roughness, such as conventional milling.