Advanced high strength steel (AHSS) is being increasingly used in automotive industries for weight reduction purposes. Hot stamping steel, which is a boron alloyed steel, has a strength greater than 1500MPa after hot forming and successive quenching. Because the heating temperature is normally greater than 900°C, a thin Al-Si based coating layer is applied to the steel surface to prevent oxidation. In this study, metallurgical characteristics of laser weldments were investigated in hot stamping steel plates with and without an Al-Si coating layer. The behavior of the Al-Si coating layer after the hot stamping process was analyzed, and the effects of Al-Si coating on laser weldability were investigated. Keyword: Al-Si coated steel; Boron-alloyed steel; Laser welding

The porosity formation in cold metal transfer (CMT) gas metal arc welding (GMAW) of zinc coated steel is studied over a wide range of the heat inputs (160–250 J mm^− 1), which shows low porosity in weld bead ( < 2% of bead area) in low ( < 250 J mm^− 1) and high (>350 J mm^− 1) heat inputs and maximum at medium (250–350 J mm^− 1) heat inputs. The high speed imaging of weld pool shows that the highest frequency of zinc vapour escapes at high heat inputs compared to other conditions. Numerous experiments show that size and location of pores along with escaping of zinc vapour are the results of competition of viscosity of weld pool against buoyancy and vapour pressure within the time required to reach solidification temperature. Based on this concept, mechanisms involved in porosity formation, growth and escape phenomena are disclosed, which can help select the optimised welding conditions to obtain porosity free welds in CMT-GMAW of zinc coated steels.

The effect of post weld heat treatment (PWHT) temperature on laser beam welds in high-entropy alloys (HEAs) using a cold-rolled cantor system (CoCrFeMnNi) was investigated. Laser welding of low heat input was applied to reduce thermal distortion. The cold-rolled HEA welds indicated larger grain size and inferior tensile/hardness properties as compared to the base metal (BM). By applying PWHT, the welds showed superior hardness to the BM with no variation in the face-centred cubic phase and a decrease in the size and fraction of CrMn oxide inclusions. As the PWHT temperature increased (800–1000°C), the variation in the grain size decreased between the weld metal and heat-affected zone, thus resulting in approximately the same tensile strength and elongation of the transverse welds as compared to the BM.