Hot forming strategy for lightweight, energy-absorbing B-pillars using 7075 aluminum alloy

The article concerns the hot stamping of the B-pillar made of 7075 aluminum alloy. The first tests were carried out on a simple U-shaped element to determine the thermoplastic treatment’s parameters. Cooling the material from 475 °C to 120 °C at a cooling rate not lower than 62.8 °C/s allowed obtaining a high-strength product (above 560 MPa, hardness above 175 HV1). The determined parameters were verified while stamping the B-pillar, and the optimization of the process allowed to obtain high dimensional and shape accuracy (below 0.5 mm in critical measurement points at the parameters of pressure 0.5 and 3 MPa) and good surface quality (roughness Ra < 0.5 μm for ester oil-based lubricant for hot forming). The changes in properties were explained by TEM microstructure studies and FEM simulations.The MgZn 2 strengthening precipitates were observed during structural tests, which confirms that all heat treatment processes (solutioning and artificial aging) were performed correctly. Three-point bending tests (crashworthiness) have proved that a hot-formed aluminum pillar absorbs the same energy as a steel pillar (made of 22MnB5, currently used in automobile bodies). A ready-to-use industrial process has been developed that enables the reliable production of any components made of 7075 aluminum.