Hot cracking in laser welds produced in metal workpieces, especially aluminum or magnesium sheet alloys, is avoided by suitably combining the beams of two different lasers, for example a CO.sub.2 laser and a YAG laser, into a compound beam that is moved along a weld path in the surface of the workpiece. The power level of at least one of the lasers is cyclically varied so that weld nugget segments of different alternating, hot crack free, configurations are produced in a linear weld.