The aluminium alloy studied in this paper is the heat treatable AA7075 which has zinc as the main alloying element. 7xxx aluminium alloys have the best strength performance among all commercial series and AA7075 has tensile strength above 500 MPa. The outstanding strength properties open the possibility to use this alloy in automotive industry as a possible alternative material for car body elements instead of steel. However, their limited formability properties mean obstacle when a complicated shape car body panel is formed, since the elongation is limited only between 5 and 11%. In order to successfully form these sheets into the demanded geometry, hot forming should be used, and thus the body panels should be formed when the AA7075 is in a solution heat treated condition, such as using the HFQ® process. Then, after assembling the body elements, when resistance spot welding is among the most common joining methods, the AA7075 body parts should get the artificial ageing. It means that welding is followed by artificial ageing as a kind of post weld heat treating which can partially compensate the softening of this alloy during welding. Softening is considered among the most challenging weldability issues similarly to the high melting point oxide layer at the surface which also reduces the load bearing capacity of RSW joints. During the performed experimental program, three routes were investigated. The RSW experiments are performed on 1-mm-thick AA7075 sheets. The spot-welded joints were examined by macroscopic testing, tensile shear and hardness tests.

The in-die quenching is a key stage in the hot stamping volume production chain which determines the post-formed strength of lightweight alloy components, tool life, and hot stamping productivity. In this paper, the performance of in-die quenching, reflected by the quenching efficiency (the time of work-piece held within stamping dies) and die surface temperature during the simulated hot stamping process of AA6082, was experimentally and analytically investigated. A range of in-die quenching experiments were performed for different initial work-piece and die temperatures, quenching pressures, work-piece thickness, and die clearances, under hot stamping conditions. In addition, a one-dimensional (1D) closed-form heat transfer model was used to calculate the die surface temperature evolution that is difficult to obtain during practical manufacture situations. The results have shown that the in-die quenching efficiency can be significantly increased by decreasing the initial work-piece and die temperatures. Die clearances are required to be designed precisely to obtain sufficiently high quenching rates and satisfying post-formed strength for hot-stamped panel components. This study systematically considered an extensive variety of influencing factors on the in-die quenching performance, which can provide practical guides for stamping tool designers and manufacture systems for hot-stamping volume production.

Near- $\alpha$ titanium alloys have extensive applications in high temperature structural components of aircrafts. To manufacture complex-shaped titanium alloy panel parts with desired microstructure and good properties, an innovative low-cost hot stamping process for titanium alloy was studied in this paper. Firstly, a series of hot tensile tests and Scanning Electron Microscope (SEM) observations were performed to investigate hot deformation characteristics and identify typical microstructural evolutions. The optimal forming temperature range is determined to be from 750 °C to 900 °C for hot stamping of TA15. In addition, a unified mechanisms-based material model for TA15 titanium alloy based on the softening mechanisms of recrystallization and damage was established, which enables to precisely predict stress-strain behaviors and potentially to be implemented into Finite Element (FE) simulations for designing the reasonable processing window of structural parts for the aerospace industry.

Driven by the demands for contactless stress detection, technologies are being used for shape control when producing cold-rolled strips. This paper presents a novel contactless stress detection technology based on a magnetoresistance sensor and the magnetoelastic effect, enabling the detection of internal stress in manufactured cold-rolled strips. An experimental device was designed and produced. Characteristics of this detection technology were investigated through experiments assisted by theoretical analysis. Theoretically, a linear correlation exists between the internal stress of strip steel and the voltage output of a magneto-resistive sensor. Therefore, for this stress detection system, the sensitivity of the stress detection was adjusted by adjusting the supply voltage of the magnetoresistance sensor, detection distance, and other relevant parameters. The stress detection experimental results showed that this detection system has good repeatability and linearity. The detection error was controlled within 1.5%. Moreover, the intrinsic factors of the detected strip steel, including thickness, carbon percentage, and crystal orientation, also affected the sensitivity of the detection system. The detection technology proposed in this research enables online contactless detection and meets the requirements for cold-rolled steel strips.

Experimental investigation and modelling of hot forming B4C/AA6061 low volume fraction reinforcement composites