CO2 and Nd : YAG laser beam welding of 6111-T4 aluminum alloy for automotive applications

There are two important trends that are currently taking place in the formi ng of sheet metal into automotive body components. One of these trends is t he substitution of aluminum sheet alloys for steel. The other trend is the use of tailor welded blanks. Currently, there exists strong motivation for research to combine these technologies in order to produce tailor welded al uminum blanks. The focus of the current study is to develop welding procedu res for autogenous CO2 (continuous mode) and Nd:YAG (continuous and pulsed mode) laser beam welding of 6111-T4-aluminum alloy. The mechanical and micr ostructural characteristics of the welded joints were evaluated using tensi le tests, microhardess tests, optical microscopy, and chemical analysis. Re sults indicate that this alloy can be autogenously laser welded with full p enetration, minimum surface discontinuities and little if any loss of magne sium through vaporization from the fusion zone. The total elongation (ali w eld metal) in the longitudinal direction for the laser welds made using 3 k W CO2 and 2 kW pulsed Nd:YAG show a decreasing trend with increasing travel speed. Studies indicate that the decreasing trend is probably due to the c ombination of two factors: orientation of the grains with respect to the lo ading direction and solidification cracking. The total elongation (all weld metal) of the laser welds made using 5 kW CO2 and 3 kW cw Nd:YAG did not s how a consistent trend with travel speed. The main reason for this is solid ification cracking. The welds made with 2 kW pulsed Nd:YAG with travel spee d between 42 and 63 mm/s displayed the highest total longitudinal elongatio n (20.78% to 16.45%), compared to the base metal values of 27.8%. A very in teresting observation was that the weld surface condition did not have any effect on the ductility of the 6111-T4-aluminum alloy studied in this inves tigation. (C) 2000 Laser Institute of America.