Abstract
To study the effects of warm laser peening (WLP) on the thermal stability and mechanical properties of A356 alloy, the samples were treated by WLP using a Nd:YAG solid-state laser and temperature control device. The residual stress, micro-hardness and microstructures of samples treated by WLP were observed. The result shows that the temperature significantly affects the strengthening effect of laser peening (LP). The residual stress induced by WLP decreases with the increasing temperature. The micro-hardness and dislocation density increase first, and then decrease with the increases of temperature. The grain refinement degree of the samples treated by WLP is much higher than that of LP. In addition, after aging for 100 min at 220 °C, the samples treated by LP and WLP were comparatively investigated in thermal stability. Obviously, the residual compressive stress, micro-hardness and microstructure induced by WLP present a better thermal stability property than that of LP. The residual stress and micro-hardness of WLP samples are obviously improved, and the increasing degrees are 23.31% and 19.70%, respectively. The dislocation density remains at a high level, while the grains are still in fine crystalline state.
Highlights
As a typical Al-Si alloy, A356 alloy plays an important role in the field of industry because of its excellent casting properties, low density, high wear resistance and low thermal expansion [1,2].A356 alloys have been widely used in cylinder heads, engine blocks and cylinder liners [3,4,5].the surface properties of A356 alloy are poor [6,7]
This paper aims to investigate the evolution of the residual stress, micro-hardness and microstructures of the A356 alloy before and after warm laser peening (WLP)
Itcan be seen that the residual compressive stress induced by laser peening at room temperature (25 C) was average about212.71 MPa
Summary
The surface properties of A356 alloy are poor [6,7]. It has been proved that the main failure modes of A356 alloy during the service process are fatigue and wear failure, which are normally initiated on the surface. Cho [13] used high energy peening to treat A356 alloy, and the results showed that after the treatment, the surface micro-hardness of A356 alloy was raised by 400% as compared to the initial matrix. Chang [14,15] investigated the mechanical properties and thermal stability of A356 alloy treated by surface alloying technology. The results showed that a nano-grain structure was discovered in the treated area after 60 min, the size of which was about 18 nm. The surface micro-hardness was raised by 80% as compared to the initial matrix. The nano-grain structure presented good thermal stability after being maintained
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