A study on mechanical properties of laser-welded blank of a boron sheet steel by laser ablation variable of Al-Si coating layer

摘要

The automobile industry has recently produced vehicle bodies using advanced high strength steel with the aim of reducing carbon emissions and developing green products. Among various processes for body manufacturing, hot stamping has been gained a remarkable consideration. In this study boron sheet steel with the initial tensile strength of 600 MPa and 22% elongation was used. The sheets were heated at 950°C for 5 min before die quenching through hot stamp forming process. After hot stamping, the tensile strength of the boron sheet steel improved and reached 1.5 GPa while the elongation markedly deceased to 7%. A very low elongation value, is not favourable in safety of automobiles since it deteriorates the shock absorption capacity upon a car accident. In order to overcome this problem, it is suggested to weld boron sheet steel with different thicknesses and make an assembly of sheets. This assembly acts as a buttress in which the lower sheet absorbs shocks. Furthermore, Al-Si coating layer has a deleterious effect on the mechanical properties of weld joints. Thus the effect of laser ablation of the coating has been thoroughly studied and discussed.