The effect of processing variables on the microstructures and properties of aluminum brazed joints

Aluminum brazed joints are used extensively in the automotive and aircraft industries. In order to insure the integrity of the bond, the effects of processing variables on the quality of the bond must be understood. The effects of brazing period and joint thickness on the microstructure, tensile properties, microhardness and micromechanisms of failure of two aluminum alloy 3003 plates connected by a layer of 4047 aluminum filler material were investigated. It was found that the amount of aluminum-silicon eutectic microstructure in the reaction zone decreased with increasing brazing period and decreasing joint thickness. This was attributed to silicon diffusion from the joint material and dissolution of base metal and its entrance into the liquid joint. The amount of shrinkage porosity in the reaction zone was found to increase with increasing brazing period due to base material solutioning. The ultimate tensile strength of joints decreased with increasing brazing period and decreasing joint thickness. This was attributed to the joint microstructure and shrinkage porosity formed in the joint. Shrinkage porosity was found to be the primary cause of decreased joint strength. Joints with 10 minutes brazing period failed within the base material, while for brazing periods greater than 10 minutes, joints failed within the aluminum-silicon eutectic microstructure of the reaction zone. This indicated that the joint strength was greater than the base material for joint with brazing period of 10 minutes. Finite element analysis was performed to determine the effect of joint material yield strength and joint thickness on the stress and strain field in the brazed joint. Finite element analysis results supported experimental observations. (C) 2002 Kluwer Academic Publishers.