Improved formability of aluminium alloys at low temperatures for automotive applicationsThursday (09.11.2017) 10:35 - 10:55 Part of:
The automotive industry is increasingly using aluminium alloys in order to reduce the total car weight and thus, decreasing CO2 emissions. Hence, for the production of complex lightweight outer panels an improved deep-drawability of aluminium alloys is required. Simultaneously, high strength levels, especially after the paint bake procedure, are requested. Here we illustrate the forming behavior of different AlMg(Mn)- and AlMgSi(Cu) alloys at room temperature and cryogenic temperatures. Tensile tests, Erichsen cupping tests and notched tensile tests - in order to obtain a multiaxial-stress state - were performed. At low temperatures, the results show an increase in uniform elongation, accompanied by a suppression of Portevin-Le Chatelier (PLC) band formation and an enhancement of the surface quality in terms of roughness and ridging. Comprehensive microstructural characterization was performed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Early stages of deformation were investigated by electron channelling contrast imaging (ECCI). With ECCI, large-scale and wide field of view investigations on bulk samples were conducted for gaining better statistical overview of the dislocation substructure evolving during deformation. In addition, the dislocation arrangement was analysed by cryogenic in-situ transmission electron microscopy (TEM) straining experiments. The method offers the possibility to study the dislocation behavior directly at low temperatures without intermediate heating to room temperature. A unique strain hardening rate was detected, which is attributed to a change in dislocation arrangement at cryogenic temperatures.