Effects of thermal aging on intermetallic compounds and properties of Cu/Al brazing joint

Cu/Al dissimilar metals were joined with Zn-22Al filler metal by torch-brazing technology and heat treated at constant temperature of 250℃ for 0 to 1000 h.To guarantee the reliability of the Cu/Al torch-brazing joints in service requirement,the growth rate of intermetallic compounds on Cu side was calculated and the effects of the intermetallic compound layer on the electrical and mechanical properties have been investigated under various annealing time.It was observed that the width of intermetallic compound increased as the thermal aging proceeded,and the growth rate of the intermetallic compound was 6.1×10¹³ cm²/s when the aging temperature was 250℃.A thicker intermetallic compound layers could degrade the resistivity and shear strength of Cu/Al joints.When the thickness of intermetallic compound was 4.2 μm and 18.1 μm,the electric resistance was 120.3 μΩ and 132.9 μΩ,respectively.Moreover,the shear strength of Cu/Al brazing joint increased by 3% when the aging time was 100 h while the strength decreased by 15% when the Cu/Al joints endured 1000 h thermal aging.