Effect Of Laser Shock Peening On Microstructures And Electrochemical Corrosion Of AZ80 Magnesium Alloy

As the lightest structural metal material, magnesium alloys have been widely applied in aerospace and automobile industry, with excellent electromagnetic shielding, heat transfer, machining properties and damping, et.al. In recent years, lightweight vehicles is considered to be one of the effective methods to deal with excessive energy consumption and serious environmental pollution, which makes magnesium alloys be more highly focused. However, the application of magnesium alloys is limited because of their low electrode potentials, poor corrosion resistances and high working environment requirements. As a new-style surface modification technology, laser shock processing has played a great superiority in improving the corrosion resistance with characteristics of strong controllability and remarkable strengthening effect. In this paper, heat treatment, the LSP experiment and electrochemical corrosion test have been carried on the rolled and as-cast AZ80 magnesium alloys. The main research content can be described as follows:Pre-solution and pre-aging treatments have been carried out on AZ80 magnesium alloy specimen, then laser shocked with two kinds of different laser pulse energy. Surface residual stress, micro-hardness, XRD and microstructures of LSP specimen are compared and discussed. The results show that high amplitude residual compressive stress is generated in the surface of LSP specimen, which increased with the increasing laser pulse energy. Micro-hardness along thickness is improved with change of gradient, and the case depth is above 1.0mm. After LSP, high density twins are generated in pre-solution specimen, but slightly observed in pre-aging samples. However, the distribution of second phase becomes more continuous and uniform.Electrochemical curves of LSP specimen in the condition of different pretreatment and different pulse energy are gained through electrochemical corrosion test, which include polarization curve and EIS curve. Corrosion resistance is discussed and electrode process occurring on the surface of magnesium alloy is simulated by fitted circuit. Combined with the analysis of microstructures and properties, the mechanism of LSP improving corrosion resistance is discussed. In addition, the best pulse energy range can be obtained in the condition of different pretreatment.Post-aging treatment has been carried out on pro-solution specimen after LSP, and the change is discussed in terms of microstructure, micro-hardness and surface residual stress. Then electrochemical corrosion test and analysis are carried out on post-aging specimen. The corrosion mechanism, the second phase precipitation and the stability of post-aging specimen are preliminarily explored.