Research On Microstructure And Properties Of Al-Ti-B Reinforced Magnesium Alloy

By these higher properties,such as resistance to wear,good plasticity,durability and an acceptable commercial price,the Mg-Al-Zn alloy is generally appreciates in industry. Compared to as-cast magnesium alloy such as wrought magnesium alloy exhibit a less casting shrinkage,hot cracking,moreover it occurs that the wrought alloy of AZ31 has better properties of plastic deformation,mechanical properties and comprehensive properties etc.In this present paper,the microstructure and proprieties of AZ31 alloy have been studied by adding two forms of Al-Ti-B.Firstly,the effects of soft-contact electromagnetic casting on microstructure and mechanical property of AZ31 magnesium alloy with different Al-5Ti-1B master alloy addition were investigated by comparing with the die cast ingot.The grain refining Performances of Al-5Ti-1B master alloy have been studied systematically on AZ31 alloy. The results show that the optimum average grain size and mechanical properties of AZ31 magnesium alloy with Al-5Ti-1B master alloy is obtained when the addition of Al-5Ti-1B master alloy is at 0.5wt.%in these experiments conditions.The average grain size is about 30 %of that of AZ31 alloy and the tensile strength and elongation are 184 MPa and 8.14%, respectively.Compared to the die cast ingot,the soft-contact EMC ingots with 0.5wt.% Al-5Ti-1B have more fine and uniform grain structure,which improves the mechanical property of magnesium alloys.The ultimate tensile strength and elongation of soft-contact EMC specimens increase by about 18%and 122%,respectively.Microstructure and mechanical properties of AZ31 alloy with Al-5Ti-1B master alloy addition are affected by Ti and TiB₂.Secondly,self-propagating high-temperature reaction mechanism of Al-Ti-B has been studied and discuss on what microstructure and mechanical properties of AZ31 magnesium alloy with Al-Ti-B addition are affected.The results show that the reaction between the various groups of Al-Ti-B thermodynamically feasible and in this case,we will see that there exist changes of TiB₂.Simultaneity in the dual-element reaction of Al-Ti-B has also been proved by differential thermal analysis(DTA).The magnesium matrix composites were fabricated with high joining ratio,uniform distribution and low pore ratio by adjusting the joining means of TiB₂ and the process parameters for the localization of recent stirring-casting technologies.Meanwhile deforming tests were performed for TiB₂ particle reinforced magnesium matrix composites prepared by stirring-casting process after hot extrusion to eliminate the defects in the structures and obtain the uniform distribution of TiB₂ particle.The structures of magnesium matrix composites and fracture surface were observed and analyzed by optical microscope and scanning electron microscope after hot extrusion.The results show that the size of grains was reduced,the uniformity of particle was improved and the connection of matrix and particles was enhanced after hot extrusion.Compared with as-cast AZ31 alloy,the hardness and tensile strength of as-cast TiB₂/AZ31 matrix composites increase slightly,but its elongation decreases.The hardness,tensile strength and wear resistance of as-extruded TiB₂/AZ31 matrix composite materials increase by 63%,25%and 20%when the addition of Al-Ti-B precast block is at 6wt.%,but its elongation decreased,and the reduced magnitude smaller than the as-cast magnesium matrix composite.