Preparation Of In-situ Particulate Reinforced Magnesium Matrix Composites Based On SHS Technology

SHS ( Self-propagating High-temperature Synthesis ) of Al-Ti-B₄C and Mg-B₂O₃-TiO₂ system are applied firstly to prepare particulate reinforced magnesium matrix composite. Based on different technical characteristics, the master alloy containing pure aluminum and ceramic particulates made from SHS reaction of Al-Ti-B₄C system is melted in molten magnesium and then the in-situ particulate reinforced magnesium matrix composite is produced. And the method of "thermal explosion + casting" that the thermal explosion of Mg-B₂O₃-TiO₂ system is happened directly in molten magnesium is used to prepare the in-situ particulate reinforced magnesium matrix composites. The thermodynamics analysis of Al-Ti-B₄C and Mg-B₂O₃-TiO₂ systems shows when Al content below 60% of Al-Ti-B₄C system and Mg addition below 70% of Mg-B₂O₃-TiO₂ system, the SHS reactions of these two kinds of systems both can be carried out by themselves and their absolutely temperatures are ascended with the starting temperatures. TiC and TiB₂ particulates can be created at 1200¹500℃ with Al-Ti-B₄C system. DTA and experiments of thermal explosion show that the Ti-B₄C reaction can be happened at a relative lower temperature by the ejective heat from Al-Ti reaction because of Al working as a catalyst in Al-Ti-B₄C system. The reaction of Mg-B₂O₃-TiO₂ system could be carried out by itself at the temperature of melting magnesium(< 800℃). Three exothermic reactions are included in Mg-B₂O₃-TiO₂ system and Mg-B₂O₃-TiO₂ reaction temperature is between Mg-B₂O₃ and Mg-TiO₂. The research of "thermal explosion + casting" technology on Mg-B₂O₃-TiO₂ system shows that stir accelerates uniform distribution of particulates; SHS reaction is promoted for prolonging the mix time; reaction starting time is shorten and SHS reaction is boosted if preheating temperature is improved; and proper heat preservation time is of benefit to form the appropriate shape of particulates. The microcosmic analysis of XRD and SEM on these two kinds of systems shows that the in-situ particulates are fine (about 2um), TiC and MgO are round and TiB₂ is square. Compared to magnesium matrix, not only tensile strength but also hardness of these two kinds of composites is improved obviously. The tensile strength and hardness of composites made from 5% Al-Ti-B₄C system are higher about 24.5% and 30% separately than magnesium matrix. The tensile strength and hardness of composites made from 5% Mg-B₂O₃-TiO₂ system are higher about 26% and 32% separately than magnesium matrix.