Investigation of the joinability of the high-strength aluminum alloy AA7075 in shear-clinching processes

Shear-clinching has proven to be a suitable technology for joining of high-strength materials. However, the mechanical properties of the upper joining partner are limited due to the high strains, which occur during the process. Therefore, shear-clinching of the high-strength aluminum alloy AA7075 in the T6 temper is not possible. Yet, the mechanical properties of hardenable alloys of the 7000 series can be influenced by a heat treatment. Thus, within the scope of this work, the joinability of the high-strength alloy AA7075 in shear-clinching processes in dependance of its temper is investigated. The as fabricated state F, the artificially aged T6 temper, a paint baked state and the naturally aged T4 temper are compared to the fully solution annealed W temper as well as to a retrogression heat-treated state. For retrogression heat treatment, a laser is used as heat source, heating up the alloy for a short term in order to only partially dissolve precipitations. The resulting mechanical properties are determined with uniaxial tensile tests. Moreover, the influence of the mechanical properties of AA7075 on the shear-clinching process, the joint formation and the resulting joint strength is analyzed.

Surface integrity and wear evolution of high strength aluminum alloy after high-speed oblique cutting

In this paper, we present an experimental study on the surface frictional wear mechanism of the high-strength aluminum alloy after high-speed milling. We use a surface profilometer and an X-ray stress tester to characterize the milled surface integrity of the material, and UMT-3 friction testing machine to obtain its surface roughness, oxygen content, hardness, and wear morphology during different wear stages. The results show that milling-induced residual tensile stress makes the cut surface more prone to fatigue cracking and consequently abrasive wear in the initial wear stage. The larger the angle between the friction pair movement direction, the greater the chance of adhesive wear and abrasive wear. A complete friction stage pattern can be obtained at a high load (15 N) and a low sliding speed (0.6 mm/s). The friction pair enters a stable wear stage after 20 sliding cycles. Work hardening constitutes the main driver of stable wear.