Research On Strengthening-toughening Of AZ61 Magnesium Alloys

In recent years, magnesium alloys have been widely used in the aerospace, war, automobile and electronic industries because of their many advantages:low density, high specific strength and stiffness, free cutting, damping capacity and recyclability. Due to hexagonal close-packed structure of magnesium alloys, their plastic is poor and the main application magnesium alloy remains die-casting. The development of wrought magnesium alloys is relatively slow, which greatly limits the development and application of magnesium alloy. So the study on strengthening-toughening of wrought magnesium alloys is the main research.In this paper, AZ61 wrought magnesium alloys are choosed as the base alloys, the technology of Ca micro-alloying, electromagnetic continuous casting, hot extrusion, heat treatment and electromagnetic-suspension forming are employed. The microstructure and mechanical properties are investigated by Metallographic microscope, XRD diffractometer, Scanning Electron Microscope, Electron Probe Microanalyser, Transmission Electron Microscope, Brinell Hardness Tester and Materias Test System. The mechanism of strengthening and toughening is explored and the relationship between microstructures and mechanical properties was studied to get the optimized strengthening-toughening treatment process.An optimized technical parameters of electromagnetic continuous casting has been obtained in this study. The AZ61 billets with electromagnetic field and microalloying have smooth surface. The result shows the electromagnetic field and Ca microalloying can refine the microstructure and improve the mechanical properties of wrought magnesium alloys: tensile strength and elongation of AZ61 alloys are 259.4MPa and 14.8%, increased by 24.2% and 32.1% respectively.Hot extrusion of Electromagnetic Continuous Casting AZ61 magnesium alloys is investigated, and the optimized technical parameters are obtained, the microstructures of as-extruded AZ61(EMCC) billets is refined, and mechanical properties are improved, tensile strength and elongation of as-extruded AZ61 alloys are 308.9MPa and 17.0% increased by 19.1% and 28.8% respectively.Heat treatment is conducted to as-extruded AZ61(EMCC) billets, the effect of different processes on the size of precipitated phase and distribution, microstructure and properties of billets were studied. The results show that after solution treatment, the crystal grain size of as-extruded AZ61(EMCC) is increased, while after ageing treatment, both discontinues and continues precipitated phasesβ-Mg17Al12 begin to form in the structure of alloy, which makes the hardness and the tensile strength improved, the maximum value is obtained at the process of 200℃+24h, the hardness and tensile strength are HB70.2 and 331.6 MPa, increased 7.0% and 7.3% respectively, while the elongation loweredTheoretical and practical complex suspension particles are designed and prepared, which are employed in the electromagnetic-suspension casting to refine the microstructure of AZ61 alloys. It shows that the complex suspension particles can be used to electromagnetic-suspension casting experiment and refine the alloy's microstructure.