Investigation of the Plane Strain Behaviour of a Laser-Heat Treated Aluminium Alloy

Abstract

The necessity of complex-shaped components characterized by superior mechanical properties and limited weight is moving the attention to the Aluminium (Al) alloys. Deep Drawing Steel grades possess superior stamping characteristics and formability with respect to Al alloys. But the need of light-weighting pushes towards the adoption of materials with optimal strenght-to-weight ratio, like Al alloys. Todays Al alloys are certainly used in the transport sector but their formability (at room temperature) is poorer than Deep Drawing Steel grades, which still hinders their massive implementation in the forming processes and drives the research toward innovative manufacturing solutions. One of the most promising approach to overcome such a limitation and, thus, manufacture complex component using cold forming processes, is the adoption of local heat treatments to obtain a suitable distribution of material properties able to enhance the formability at room temperature.The design of cold forming using locally modified blanks needs: (i) an extensive investigation of the material behaviour at room temperature after the local heating and (ii) the adoption of a Finite Element approach. As for the former aspect, the authors proposed a fast and comprehensive methodology to investigate the hardening behaviour of an Al alloy (AA5754-H32) locally annealed by laser heat treatment. Using a similar approach, the hardening model was then enriched by considering the normal anisotropy, evaluating the correlation between the Lankford parameter and the material condition reached at the end of the local treatment. To improve the knowledge on the plastic response of the material, the present work focusses on the characterization of the plane strain behavior of the AA5754, initially in wrought condition (H32) and subsequently modified by laser heating. In particular, the study proposes a new quasi-homogeneous specimen which combines the local heating profile with an optimized geometry to produce a prevailing plane strain condition in the heat-treated zone. In such a way, data about the material response in the plane strain condition could be obtained for a large range of material conditions determined by the preliminary heat treatment.