Abstract
The aim of this paper is to study the effects of laser peening (LP) on the residual stress distribution and microstructure evolution of AA 6061-T6 under different temperatures. A laser peening experiment was conducted on the square-shape samples by using single spot and 50% overlap shock. Three-dimensional surface morphologies of treated samples were observed. The influence of peening temperature on the distribution of compressive residual stress was analyzed. An optical microscope (OM) and a transmission electron microscope (TEM) were employed to observe the microstructure evolution of the samples before and after LP. The results indicate that, as the peening temperature increases, the micro-hardness increases first and then decreases. The LP process induces high-amplitude compressive residual stress on the surface at different temperatures even if the compressive residual stress slightly reduces with increases in temperature. The maximum compressive residual stress affected layer depth is about 0.67 mm, appearing at a temperature of 160 °C. The OM test revealed that the grain size was significantly decreased after warm laser peening (WLP) and that the average value of grain size was reduced by 50%. The TEM test shows that more dislocation tangles were produced in AA 6061-T6 after WLP; compared to the LP process, the precipitate-dislocation interaction can benefit both strength and ductility for AA 6061-T6, thus enhancing the mechanical properties of the material.
Highlights
AA 6061-T6 is an Al–Mg–Si–Cu alloy which is widely used in aerospace industry, ship manufacturing, and rail truck fields due to its high strength, good plasticity, and good performance in weldability and corrosion resistance
The results showed that laser peening (LP) is an effective surface treatment technique that can induce beneficial compressive residual stress and microstructures, such as a high density of dislocation, mechanical twins, and refined grains, which eventually retards fatigue crack growth
LP-produced circle-shape dents are observed in all cases
Summary
AA 6061-T6 is an Al–Mg–Si–Cu alloy which is widely used in aerospace industry, ship manufacturing, and rail truck fields due to its high strength, good plasticity, and good performance in weldability and corrosion resistance. It has been found that micro cracks are likely to occur on the AA 6061-T6 surface at a specific strain rate and service temperature, resulting in fatigue failure [1]. The need to employ new technology to improve the mechanical properties, in particular the surface performance, and prolong the fatigue life of AA 6061-T6 alloy parts is worth the necessary attention. LP utilizes a high-intensity laser pulse on the metal surface, which is covered by an absorbing layer (black tape or aluminum foil) and a confining layer (water or glass), respectively. A laser pulse passes through the confining layer and hits the target surface, which is immediately vaporized and forms the plasma. The resulting plasma is confined by the confining layer and generates an extremely high amplitude of pressure of several GPa. As the peak pressure exceeds the dynamic yield
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