An Investigation on Microstructure and Mechanical Properties of Nd:YAG Laser Beam Weld of Copper Beryllium Alloy

Nd:YAG pulsed laser beam welding is conducted on UNS-C17200 copper beryllium sheet. Welding is carried out in the as-annealed and as-aged conditions to investigate the effects of preweld condition on weld microstructure and mechanical properties. Two different heat treatments including direct age treating and solution annealing + subsequent age treating are considered after welding. The mechanical and microstructural characteristics of weld metal regions (WMs) and heat-affected zones (HAZ) of four different samples are considered using tensile tests, hardness measurements, optical microscopy, electron microscopy, and X-ray diffraction (XRD). Results indicate that the microstructural and mechanical properties of the HAZ without postweld treatment are adversely affected by grain boundary liquation observed if welding is carried out in the as-aged condition. Tensile strength and hardness of the WM are improved after a postweld artificial age treatment at 315 °C for 3 hours. However, hardness of the WM is lower than that of the base metal (BM) and HAZ, because the precipitation mechanism in the fusion zone is not as effective as that is in the HAZ and BM. The CuBe secondary phase precipitates during solidification. The precipitates/matrix interface is incoherent, which does not significantly raise the hardness of the weld metal. Incoherent interdendritic precipitates are dissolved in the weld structure after postweld solution annealing. Having performed postweld solution treatment and aging, full strength and hardness throughout the copper beryllium material were observed.