Effect of Alloy Elements on the Microstructure and Properties of Al-base Solder

Alloy composition of low melting-point Al-Si-Cu-Mg solder is designed with orthogonal experiment, the microstructure and properties of the solder are analyzed by means of metallographic examination, hardness measurement, spreadability and differential thermal test method. The results show that the microstructure of solder brazing is mainly composed of matrix phase α -Al, granular phase Mg₂Si, skeletal shape phase Al₂Cu (θ phase), and the θ phase and Mg₂Si complex eutectic. Effects of alloying elements on microhardness and melting characteristic from primary to secondary are: Cu, Si, Mg. Affected by intermetallic compound Al₂Cu and Mg₂Si as well as the precipitation of primary crystal Si, the spreading areas of solder change little after the contents of Cu, Si reach a certain value (10%Cu, 7.5%Si). And as for the Al-7.5Si-20Cu-0.4Mg at melting-point 529℃, the spreading area get larger and the combination properties is good in experimental formula.