In Situ Synthesis Of Mg <sub> 2 </ Sub> Si / Al Composite Microstructure And Mechanical Properties

In this paper, the Mg₂Si/Al composites with different content of Mg₂Si have been produced using in-situ synthetic method by adding certain content of Mg and Si elements. The processing parameter of Mg₂Si/Al composites has been studied by orthogonal experimental design, and the primary Mg₂Si particles have been modified by the P, Sb, Re and extra Si addition. The testing of microstructure observation, hardness, strength, impact toughness and wear resistance of composites modified with different processes have been conducted. The modification mechanisms of the primary Mg₂Si particles and the influence on the mechanical properties and wear resistance of the composites have also been studied. The results show that:The content of Mg₂Si has a bigger effect on the size of primary Mg₂Si, and holding time and pouring temperature have some influence on the morphology of primary Mg₂Si. The processing parameters that composites with the optimal modification effect of the primary Mg₂Si particles as following: the content of Mg₂Si in composites is 10wt.%, holding time is 15 minutes, pouring temperature is 765°C.The addition of extra Si, P and Sb elements can effectively modify the primary Mg₂Si of 20wt. % Mg₂Si/Al composites. The size of primary Mg₂Si is decreased gradually and the morphology is improved with increasing the content of alloying elements. The addition of 5wt.% extra Si or 0.5wt.% P element make the primary Mg₂Si has the optimal modification effect. The size of the primary Mg₂Si is finest and the morphology is changed to small dendrite or particles from coarse dendrite. Addition to the modification to the primary Mg₂Si, the Sb can effectively modify the eutectic structure. The better complex modification effect of primary Mg₂Si and eutectic structure is obtained after adding 0.4wt.%Sb. The combine addition of Sb and Re has also better modification effect on the primary Mg₂Si. The suit content of Sb and Re is 0.6wt.% and 0.8wt. % respectively.The addition of the extra Si, P and Sb elements can obviously improve the mechanical properties of 20wt.% Mg₂Si/Al composites. The highest hardness of the composites can be obtained. The composites with 0.5wt.% P or 0.4wt.% Sb have the highest hardness and ultra tensile strength (UTS). Addition to this, the addition of 0.4wt.% Sb can make the composite have the optimal impact toughness. Ti element in low-titanium aluminum is beneficial to improve the strength and impact toughness of the composites. The observation of the fractography morphologies of the tensile and impact samples shows that the fracture of composites is brittle mode. The cleavage fracture of Mg₂Si is the basic fracture mechanism of the composites.The composites with 5wt.% extra Si and 0.4wt.% Sb have optimal wear resistance. The wear resistance of the composites which produced by low-titanium aluminum are better than that of other composites which produced by pure aluminum. The improvement of the wear resistance by alloy elements is related to the modification of the Mg₂Si particles and enhancement of the matrix. The main wear mechanism is grain-abrasion and oxide-abrasion.