Microstructure And Properties Of Mg₂Si/AZ91D Composites Fabricated Under Ultrasonic Field

Magnesium matrix composites reinforced by Mg₂Si particles have been synthesized successfully by direct melt reaction method from AZ91D-Al₂(SiO₃)₃ system.The solidification structures,mechanical properties and wear performances of composites as well as the sizes,morphologies and distributions of the particles are investigated by using measurements of X-ray Diffraction(XRD),Optical Microscope (OM),Scanning Electron Microscope(SEM),Energy Dispersive Spectrometer(EDS) and so on.The mechanisms of these characteristics have been discussed.The results show that the solidification structures of composites are affected by the content of Al₂(SiO₃)₃.The solidification structures of matrix alloy can be refined. When Al₂(SiO₃)₃ content is less than 2wt.%,the Mg₂Si particles show mainly needle and long strip shapes.Theα-Mg phases in solidification structures of matirx alloy become coarsening,and the sizes of Mg₂Si particles in irregular-shape become large when Al₂(SiO₃)₃ content is 3wt.%.However,when Al₂(SiO₃)₃ content reaches 4wt.%, theα-Mg phases become more coarsening as well as the size of Mg₂Si particles,the particles present bulk-shape.Sr,Ba and Ce can refine the solidification structures, change the shape and decrease the size of Mg₂Si.When adding Sr,Ba and Ce simultaneously,the grain-refining effect is the best.Under high intensity ultrasonic applying,the solidification structures of composites as well as the size and shape of Mg₂Si are finer,and the modification function is the best when the ultrasonic treatment time and power are 7min and 1.2kW,respectively..The results of the mechanical properties testing of the composites show that,the tensile strength of composites is obviously increased with the increase of the content of Al₂(SiO₃)₃,and the elongation is reduced.When the Al₂(SiO₃)₃ content is 3wt.%, the tensile strength reaches 178.6MPa.With the addition of Sr,Ba and Ce,the tensile strength and elongation of AZ91D alloys and Mg₂Si/AZ91D composites can be improved.In the case of simultaneous adding Sr,Ba and Ce,the tensile strength and elongation of the matrix alloy and composites reach to 195.4MPa,1.86%and 210.2MPa,1.79%respectively.The high intensity ultrasonic can improve tensile strength and elongation of composites,the tensile strength reaches to 206.1MPa when the ultrasonic treatment time and power are 7min and 1.2kW respectively. The results of the wear performances testing of the composites show that,with the increase of the content of Al₂(SiO₃)₃,the wear weight losses are reduced.When adding 3 wt.%Al₂(SiO₃)₃ into AZ91D,the wear weight loss is reduced 98.3%to the matrix alloy.When the content of Al₂(SiO₃)₃ is 4wt.%,the wear weight loss is stable at around 98.3%.The wear mechanism is adherence wear and abrasion wear.