Microstructure And Mechanical Properties Of TIG Welded Magnesium Matrix Composite (TiCp/AZ91) Joints

With the rapid development of advanced technology, composite materials are applied widely in aerospace, automobile, general machine, and architecture for its wonderful combination property. And composite materials are also pefect in future exploitation of new energy sources. At present, composite material is vest in four main mateterials with metal material, nonmental material and macromolecule material. Metal matrix material is the most promising one among the composite materials, in which particulate reinforced aluminium matrix composite has been commercialized. Magnesium matrix composite, which has lower density, higher strength ratio and rigidity ratio, could be used widespread. Since the cost of magenesium matrix composite has been reduced gradually,it's reasonable that magnesium matrix composite which has a lot of advantages will be in vogue. However, the application of any advanced material not only depends on its own properties, but also relies on the technologies of material manufacturing, the welding is just one of the most important material manufacturing. Fusion welding, especially TIG (tungsten inert gas), is universal in industry. And aluminium matrix composite has been joined by TIG. For the precedent of aluminium matrix composite, we chose TIG as method of joining TiCp/AZ91. However, there are some disadvantages of fusion welding to bond particulate reinforced magenesium matrix composite, such as blow holes , incomplete penetration, incomplete fusion, reinforcements segregation, these welding defects would come into being because of the high melting point TiC. Besides, the matrix metal AZ91 would react in brittle intermetallic compound Mg17Al12. These problems should be resolved by chosing proper welding materials and parameters. At last, the welded joints should achieve satisfying mechanical properties: strength, hardness, and wear resistance.In this paper, effects of three different weld compositions(AZ31,AZ61 and TiCp/AZ91 Wires) on microstructures and mechanical properties of TIG welded TiCp /AZ91 magnesium matrix composite joints have been investigated.Some conclusions have been drawn as follows:(1) Welded joints of TiCp/AZ91 magnesium matrix composites include welding zone(WZ), heat affected zone(HAZ) and the base zone metal zone(BZ). The size of WZ is small, the size of BZ grains is coarser, and the size of HAZ grains is close to BZ. The microstructure of TiCp /AZ91 BZ and TiCp/AZ91 WZ are primaryα-Mg, eutecticβ-Al12Mg17 and reinforcements TiC. However, the distribution of TiC in Homogeneity WZ is more uniform. The microstructure of AZ61 WZ isα-Mg andβ-Al 12 Mg17. The microstructure of AZ31 WZ is mainlyα-Mg. Liquefaction of grain boundaries in HAZ is also very important phenomena.(2) There are some porosities in three welds, and the TiCp/AZ91 WZ has the largest amounts of porosities. The appearances of porosities observed by SEM are different from normal hydrogen porosities, the internal surface is not smooth, and some particles can be observed on the surface,these particles should be TiC. (3) The microhardness of homogeneity WZ is higher than base metal, the microhardness of AZ61 is a bit lower than basic metal, and the microhardeness of AZ31 is much lower than basic metal. However, there is an obvious decrease in microhardness in HAZ of all three joints. Because the tensile fractures of joints locate on HAZ or porosities, the strength of three joints is very low.