The previous investigations show that the maximum tensile strength of welded joint by plasma arc in-situ weld-alloying of SiCp/6061Al MMCs with titanium sheet filler is 220 MPa. The maximum tensile strength of welded joint with Ti-60Al alloy sheet filler is 235 MPa, which shows that the filler of Al-Ti improves the mechanical properties of joints.
Fig.1 shows a typical fractograph of welded joint by plasma arc in-situ weld-alloying with Ti-60Al alloy filler. A careful inspection of the fracture surface shows that the fracture occurs in the centre of the weld joints. The sheet area, induced by the avulsion of Al3Ti phases from basal body, shows the brittle fracture, and the others is ductile.
The particle segregation and excessively bulky Al3Ti phases in the weld undoubtedly have negative effect on the mechanical properties of welded joint. As well known, the interface layer between the wild phases and metal matrix is the key factor that affects the performance of welded joint of composite material. The condition of the interface layer, by which the load on the welded joint transits from the metal matrix Al to the reinforcement particles, is the key factor that influences the mechanical property of composite material. The defect of particle segregation breaks the interface layer and becomes the crack source debasing the joint strength under the effect of tension stress. The long strip- like Al3Ti phase penetrates the crystal grains and could break the continuity of metal matrix. So the joint strength still can not reach the level of the mother material.
Fig.1 Microfractograph of welded joint with Ti-60Al alloy sheet filler
It can be inferred that the factors which influence the tensile strength of welded joint produced by plasma arc in-situ weld-alloying on SiCp/6061Al MMCs with Ti-60Al alloy filler are mainly the particle segregation and excessively bulky Al3Ti phase in the weld.
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