Microstructural investigations on laser welded Al-30wt.% B4C composite

In order to tailor the microstructures and mechanical properties of laser welded Al-B4C composite, it is necessary to elucidate the chemical reactions between B4C reinforcement and Al matrix during laser welding process. In this study, 3 mm thick Al-30wt.% B4C plates were laser welded using different parameters. Then the microstructure, reaction products, tensile properties and fracture surface of welded joint were studied. The results show that the reaction products of the weld zone can be controlled by varying the welding energy input, but the full penetration welded joint requires high energy input (120 KJ/m in this paper). For the full penetration welded joint, all B4C particles and part Al matrix react to form irregularly particle-like AlB2C2 and coarse needle-like Al4C3 phases, the joint efficiency is 67%. The failure mechanism of AlB12C2 is cleavage fracture, and the failure mechanism of Al4C3 is interfacial decohesion and pull out. The interfacial decohesion between Al4C3 and Al matrix results in crack initiation due to their weak bonding interface. The cracks propagate, connect and penetrate the brittle AlB12C2 phase and eventually lead to brittle fracture of the joint.