Effect of Si contents of core and filler alloys on brazeability of aluminum clad fins

摘要

The brazing behavior of aluminum clad fin with thickness from 60 to 80 mu m for automotive heat exchangers was studied in order to improve the fillet forming ability which usually declines with reduction of fin thickness. Three types of core alloys (Al-l.2 mass percent Mn-0.06 approx 0.57 mass percent Si-1.5 mass percent Zn) and four types of filler metals (Al-7.35 approx 9.50 mass percent Si) were used. The fillet area, formed on the fin and tube joints, increased with increasing the silicon content of both core alloys and filler metals. The result was caused by the diffusion of silicon from the filler into the core alloy during the heating processes of intermediate annealing and brazing. Consequently, the reduction of silicon concentration in filler metal became small with the increase in the silicon content of core alloy. The flow factor decreased with decreasing the fin thickness due to the residual filler with constant quantity on the surface of clad fin. The fillet area tended to increase in proportion to the average concentration of silicon in clad fin. Then, the fillet was not formed at the low silicon concentration, whereas the fin deformed due to the erosion of core alloy contacting with molten filler metal at the high silicon concentration.