Restraint effects in laser welding of an aluminum MMC

Laser beam welding (LBW) of an aluminium metal matrix composite (alloy A40) with a low coefficient of thermal expansion has been investigated. It was found that the cracking propensity of this alloy when laser welded is affected considerably by the restraint conditions at the weld joint. A low restraint joint geometry was chosen that resulted in the completion of crack free alloy A40 welds using the pulsed Nd:YAG LBW process. In contrast, similarly processed welds made in a high restraint weld joint were found to be cracked after welding. The cracks were determined to be solid state cracks and no solidification cracking was indicated. High restraint weld joints between alloy A40 and aluminum alloys 6061 and 1100 were welded crack free. The absence of cracking here was attributed to the high ductility of these alloys which can better accommodate the weld induced shrinkage strains than alloy A40 by itself. It was found that alloy A40 has good absorptivity with the low continuous power CO2 LBW process, and that unlike pulsed laser welds in a high restraint joint geometry, the continuous power welds are crack free