Research On Preparation And Microstructure Mechanical Properties Of In Situ Al/TiB₂Composites

In situ AI/T1B2composites have been extensively studied due to their high specific strength, good thermal stability. They can be used as potential materials for specific applications in automobile, chemical, aerospace and transportation industries. Among various methods to fabricate in situ AI/T1B2composites, that which involves the halide salt reactions is the most popular.In this paper, the effects of addition sequence and additive form of the halide salts on the microstructures of AI/T1B2composites were studied. The interaction between T1B2particles and the eutectic Si, oc-Al in Al-Si/TiB2composites were also studied. Using different reaction temperatures, holding times and stirring technics, the composites thus obtained will have distinct microstructures, resulting in different comprehensive properties. In this work, we first optimized the processing parameters of the conventional halide salt method.The optimized in situ AI/T1B2composites were prepared by adding the pre-mixed K2T1F6and KBF4salts gently into the molten aluminum. The TiB2particles were severely agglomerated when adding blocks of mixed halide salts into the melt though it can facilitate the reaction. The in situ T1B2particles can modify eutectic Si in some extent and change its morphology to, to say the least, spherical. The interaction between TiB2particles and the Si leads to a reduction in the TiB2particle size. The average particle size of TiB2was reduced from above1μm to below0.5μm as the Si content increased from5%to10%.An improved halide salt route was developed to fabricate in situ TiB2particulate reinforced aluminum matrix composites using mechanical stirring. The results show that850℃is needed to facilitate the reaction process and holding the melt for60min produces Al/TiB2composite with sound tensile properties. Stirring during reaction was found to degrade the mechanical performance of the final product. A higher mechanical stirring helps to scatter the in situ T1B2clusters while hurting the element recoveries in the as-received composites. The experimental Al-5TiB2composite, prepared under the improved halide salt route, has achieved a161%improvement in the UTS without compromising its ductility with respect to the Al matrix.Pre-milling methods were introduced to prepare in situ AI/T1B2composites and the size of in situ formed TiB2particles was successfully reduced to satisfy the Orowan strengthening mechanism (finer than500nm) using the pre-milling treatment. The effects of the milling and sintering processes on the particulate size of TiB2in situ formed were also discussed. The performances of the submicron or even nano-particulate reinforced aluminum matrix composites fabricated by pre-milling method were excellent.