CO 2 and Nd:YAG laser beam welding of 6111-T4 aluminum alloy for automotive applications

Abstract

CO 2 laser beam welding of AM60 magnesium-based alloyThere are two important trends that are currently taking place in the forming of sheet metal into automotive body components. One of these trends is the 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 aluminum blanks. The focus of the current study is to develop welding procedures for autogenous CO 2 ͑continuous mode͒ and Nd:YAG ͑continuous and pulsed mode͒ laser beam welding of 6111-T4-aluminum alloy. The mechanical and microstructural characteristics of the welded joints were evaluated using tensile tests, microhardess 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 vaporization from the fusion zone. The total elongation ͑all weld metal͒ in the longitudinal direction for the laser welds made using 3 kW CO 2 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 combination of two factors: orientation of the grains with respect to the loading direction and solidification cracking. The total elongation ͑all weld metal͒ of the laser welds made using 5 kW CO 2 and 3 kW cw Nd:YAG did not show a consistent trend with travel speed. The main reason for this is solidification cracking. The welds made with 2 kW pulsed Nd:YAG with travel speed between 42 and 63 mm/s displayed the highest total longitudinal elongation ͑20.78% to 16.45%͒, compared to the base metal values of 27.8%. A very interesting observation was that the weld surface condition did not have any effect on the ductility of the 6111-T4-aluminum alloy studied in this investigation.

Inherent instability investigation for low speed laser welding of aluminum using a single-mode fiber laser

“…Also, a 4.5 kW CO 2 laser produced penetration depths of 3.5 mm in aluminum alloy series 5000 (non heat-treatable) and 6000 (heat-treatable), at a speed of approximately 33 mm/s; in comparison, a 4 kW Nd:YAG laser produced weld depths of 4 mm at the same speed (Cao et al., 2003). In addition, Ramasamy and Albright (2000) showed that when welding with a pulsed 2 kW Nd:YAG, or a 3 kW continuous wave Nd:YAG, or a 3-5 kW CO 2 laser, vaporization of magnesium and/or silicon could occur from aluminum alloy 6111-T4 and also the metal hardness was reduced. This means that when operating at very high power densities, loss of alloying elements is a significant problem.…”

A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing, microstructure, and properties

“…The change in the chemical composition of the laser processed part is a function of the vaporisation rate and the volume of the molten pool [185,186]. Although, alloying vaporisation rate increases with the dissipated energy density, the change in composition is most pronounced at low energy density levels due to small size, and the high surface-to-volume ratio, of the molten pool [185,186]. Therefore, employing laser processing conditions combining medium or high power with high scanning rates is critical to avoiding alloying vaporisation [184].…”

Investigation of weld defects in friction-stir welding and fusion welding of aluminium alloys

“…The presence of Mg is very important in 5000 series and 6000 series alloys; as is Zn in 7000 series alloys (Cross et al 2003). Ramasamy and Albright (2000) found that vaporisation of magnesium and silicon occurred and metal hardness was reduced in welding of aluminium alloy 6111-T4 with a 2-kW Nd:YAG laser in the pulsed mode, a 3 kW continuous wave Nd:YAG laser, or a 3-5 kW CO 2 laser.…”