THE EFFECTS OF TRACE ELEMENTS ON Al-Si EUTECTIC BRAZING FILLER METAL

In this paper,systematic investigation has been made on the effects of Na,Sr,MR (mischmetal),La,Co,and Bi on Al-Si eutectic filler metal.The mechanism and the conditions for maintaining modified structure in fillet,and the causes of improved mechanical propertles and corrosion resistance of the brazed joint have been studied.The authors come to the conclution that 1. With modified filler metal,the mechanical properties and corrosion resistance of brazed joint can be improved.The Al-Si eutectic filler metal modified with sodium salt,due to its excellent properties and low cost and also to the maturity of modifying process with such salt,is recommended as a new high-melting point filler metal for aluminium.2. Under the conditions of brazing,the maintaining of modified structure in the fillet is due to the special "inheritance" of Al-Si alloy,not to the function of "along effective" modification.3. The poor bending property of joints brazed with common Al-Si filler metal results from the crack propagation along the coarse Si phase.After modification,the Si is refined and the crack propagation checked,resulting in higher strength and better plasticity of the joint.4. After modification corrosion resistance of brazed joint is increased because of refinement of eutectic structure in the joint.