Experimental Researches On Friction Stir Welding And Pulsed Laser Welding Of High-silicon Aluminum Alloy

Due to its low density, low linear expansion coefficient and high specific strength, high-silicon aluminum alloy was widely used in electronic packaging field. However, a large number of silicon particles existed in high-silicon aluminum alloy, as a result, the welding performance was poor, with high tendency to crack.Pulsed laser welding method was conducted on joining of Al-27Si, and the effects of welding parameters, such as welding current, welding travel speed rate, laser pulse width and laser frequency on surface quality and welding pool shape were systematically analyzed. The results showed that the weld penetration increased with increasing of welding current, laser width and frequency due to enhancement of welding heat input. However, the weld penetration decreased and inter-ripple distance increased with increasing of welding travel speed. Consequently, good weld joint could be obtained with optimal welding criterion (welding current of 90A, pulsed width of 2ms, laser frequency of 30Hz, and welding travel speed of 200mm/min).Then, friction stir welding method was respectively conducted on joining of Al-27Si and Al-50Si. The results showed that the FSW joint was composed of base metal, nugget zone, shoulder-affected zone and thermal-mechanical affected zone. a-Al matrix and large silicon particles were observed within base metal, the microstructure of nugget zone consisted of small amount of a-Al matrix and dispersively distributed fine Si particles, the dimension of Si particles in shoulder-affected zone was smaller than that of nugget zone, thermal-mechanical affected zone lied in transition region of nugget zone and base metal, in which Si particles were fined as well. The results indicated that the increasing of rotating speed resulted in significant’origin-rings’ shape, increasing of micro-hardness and the amount of fine Si particles. The average of micro-hardness of nugget zone was 220HVo.2 with rotating speed of 1200r/min, 100HV0.2 higher than that of base metal. The refining effect of Si particles was considered to be the main reason that caused the increasing of micro-hardness. The decreasing of welding travel speed rate resulted in dimension reduction of Si particles in different areas. Superior joint of Al-27Si and Al-50Si alloy could be obtained with optimal welding criterion (rotating speed of 1200r/min, welding travel speed rate of 50mm/min, plunge depth of 0.2mm).In the dissimilar friction stir welding of Al-27Si and Al-50Si, study on FSW process of dissimilar Al-27Si and Al-50Si showed that good surface quality and less flash could be obtained with Al-27Si lied in the advanced side. The decreasing of welding travel speed rate could effectively improve the inhomogeneous phenomenon in nugget zone and shoulder-affected zone. However, surface quality with Al-50Si lied in the advanced side was poor. The inhomogeneous phenomenon couldn’t get improved with the decreasing of welding travel speed rate.