Residual stress analysis in Al-50Si alloy after laser beam welding by X-ray diffraction

Al-50Si alloy sheets with 1 mm thickness were welded using a 500 W Nd:YAG laser system. The effects of welding pulse frequency on surface welding seam morphology, microstructure and residual stresses were investigated. The narrow welding seam and underfill defects were observed after welding at 5-35 Hz pulse frequency. Depth of welding seam increases when pulse frequency was increased. X-ray diffraction method was used for residual stress measurement. The state of residual stresses in fusion zone is tensile, while that in matrix material is compressive. The highest tensile stress value is located in the welding centreline for all the samples after welding at 5-35 Hz. For the sample after welding at 5 Hz pulse frequency, the value of tensile stresses in welding seam centreline is 230 MPa, and for the sample after welding at 35 Hz pulse frequency, the value of tensile stresses in welding seam centreline is 157 MPa. Generally, the value of tensile stresses in welding seam increases when welding pulse frequency was increased, while the value of compressive stresses in matrix materials almost keeps invariable when welding pulse frequency was increased.