Microstructure and microhardness of hot extruded 7075 aluminum alloy micro-gear

Micro-gear is an important actuating component used widely in micro-electromechanical-systems. It is important to develop microforming techniques for micro-gears manufactured from high-strength commercial alloys. In this work, micro-gear extrusion of the high-strength commercial 7075 aluminum alloy (yield stress > 460 MPa) was successfully performed. The effects of extrusion temperature, extrusion velocity, and lubrication conditions on the formability, microstructure, and micro-hardness of the 7075 aluminum alloy were studied. The experimental extrusion load was larger than that predicted by finite element (FE) analysis, because of the temperature drop and friction conditions. Better lubrication and elevated temperatures caused a marked decline in the extrusion pressure, and improved the gear surface quality. The microstructural differences depended on the location within the sample as well as extrusion conditions. Higher microhardness was observed at a lower extrusion temperature or in the central region or under lubrication extrusion, which can be explained by the differences of microstructure, dislocation density, strains distribution, and second-phase particles in these specimens. The microhardness distribution in the gears was contrary to that in micropart extruded at room temperature.