Study On Surface Strengthening Method Of7075Aluminum Alloy

Aluminum and aluminum alloys is widely used in aerospace, auto-industries machine, etc due to their outstanding properties, including light weight, excellent strength-to-weight ratio and high corrosion resistance. However, in most of the time failures of these materials occur on the surface owing to the low hardness and poor wear resistance, which restrict the wider application of aluminum and aluminum alloys. As a result, some traditional surface treatment technology is used in improving the surface properties, such as:electroless nickel plating, nitriding, thermal diffusing permeation etc. Optimization of the process of traditional technology had received considerable interests in the recent decade.In this work, the process of electroless nickel plating with nitriding treatment as well as interdiffusion between7075and Mg-Zn alloy were studied by means of optical microscopy, X-ray diffraction, scanning electron microscope, microhardness tester. The main results include:(1) Experimental evidences showed that a nickel plated layer was obtained on the surface of7075alloys, the thickness of nickel plated layer increased with increasing treatment time. After nitridng treatment for nickel plated sample, some nitrides such as Ni4N, Al3Ni, Al3N2compound formed by means of interdiffusion of Ni and Al were found in this process, Moreover, the amount of compounds increased with increasing the treatment time. The hardness of the surface layer increased significantly with a value of700HV, which is much higher than that of conventional7075alloy.(2) Rusult of annealing on interdiffusion between7075alloy and Mg-Zn alloy:the diffusion layer of different Al-Mg-Zn alloy phase was obtained in the diffusion region, after annealing at460℃for10min. The hardness of diffusion layer was up to240HV, twice higher than that of7075alloy matrix; the diffusion layer was composed of eutectic structure of Al-Mg-Zn and Al-Mg-Zn phase with high content of Zn when annealing was porformed at470℃for60min. The hardness of diffusion layer increased significantly with a value of77.2HV.