Process analysis and microstructural influences during contact heating of aluminium

In order to increase the energy efficiency of transportation, the mobility market is increasingly focusing on weight reduction. It is anticipated that the proportion of aluminium alloys in the mobility sector will continue to increase. High-strength aluminium alloys and next generation alloys with increasing amounts of secondary aluminium require the development of energy and cost efficient heat treatment technologies for the thermomechanical treatment of sheet metal material. Contact heating as a rapid heating process can be a promising technological approach to efficiently preheat aluminium components for subsequent temperature assisted forming processes. This paper focuses on the analysis of the different influencing factors during the contact heating process and the investigation of the influence of the microstructure of the aluminium alloys on the heating process. Based on preliminary investigations [1], a full-scale contact heating tool has been developed which has been used to study aluminium sheets with thicknesses between 1.0 mm and 5.2 mm at various temperatures, highly thermally conductive contact plate materials (CuCr1Zr and CuZn39Pb3) and surface pressures between 3 MPa - 15 MPa. The investigation of the high-strength aluminium alloy EN AW-7075 revealed that the heating rates are predominantly influenced by the thermal conductivity of the contact plate materials rather than by the surface pressures. Furthermore, it was determined that sheets with coarse-grained microstructures exhibit faster heating rates. The study also successfully demonstrated the feasibility of the contact heating concept with highly thermally conductive contact plates for larger components (300 x 300 mm), which emphasises the future usability of the heating process for subsequent forming processes for larger components.