CO2 and Nd–YAG laser beam welding of 5754–O aluminium alloy for automotive applications

Abstract

Federal regulations have recently been enacted to reduce significantly the atmospheric pollution caused by motor vehicles. This has compelled automotive manufacturers to improve the fuel efficiency of cars and light trucks by using lightweight materials such as aluminium. The focus of the present work is to develop welding procedures for autogenous CO₂ (continuous mode) and Nd–YAG (continuous mode) laser beam welding of 5754–O aluminium alloy. The mechanical and microstructural characteristics of the welded joints were evaluated using tensile tests, microhardness tests, optical microscopy, and chemical analysis. Results indicate that this alloy can be autogenously laser welded with full penetration, minimum surface discontinuities, and little if any loss of magnesium through vaporisation from the fusion zone. The total elongation (all weld metal) in the longitudinal direction for 5754–O laser welds produced using 5 kW CO₂ and 3 kW continuous wave (CW) Nd–YAG shows a slight decrease with increasing travel speed. Studies indicate that the decreasing tendency is probably due to the orientation of the grains with respect to the loading direction. The welds produced using the 5 kW CO₂ laser at travel speeds between 127 and 212 mm s^-1 displayed a total longitudinal elongation of 19.13–15.12% and those produced using the 3 kW CW Nd–YAG laser at travel speeds between 85 and 148 mm s^-1 displayed a total longitudinal elongation of 22.6–18.15%, compared with the base metal value of 28.1%. An observation of great interest was that the weld surface condition did not have any effect on the ductility of the 5754–O aluminium alloy studied in the present investigation.