Study On The Microstructures And Mechanical Properties Of Heat-resistant RE Magnesium Alloys With Low-cost

Magnesium alloys have many advantages, such as low density, high specific strength, good damping properties, but its high temperature mechanical performance is poor, and this severely restricts the development and applications of magnesium alloys. Adding expensive elements Ag, Th can effectively improve the heat resistance of magnesium alloys, bur it is difficult to be accepted by the automotive industry because of the high-cost. Therefore, the development of low-cost and excellent high-temperature mechanical properties of the heat-resistant magnesium alloys has became an important direction of magnesium alloys research.To solve above problems, this thesis selects two common AZ91 and WE43 commercial magnesium alloys as research objects, and designs two routes to develop low-cost commercial heat-resistant magnesium alloys:1. Improving microstructure of AZ91 magnesium alloys. In this experiment, adding microscale and relatively inexpensive rare-earth elements La and Ce to AZ91 magnesium alloys. In addition, adding a small amount of Ca and Si can reduce the single element’s high cost. Subsequently using solid solution aging treatment and extrusion process to improve the high temperature mechanical properties of the magnesium alloys.The experimental results show that: Adding elements La, Ce, Ca and Si can effectively reduce the grain size of cast AZ91-X alloys. Through room temperature tensile test, the tensile strength of extrusion peak-aged AZ91-X alloys is 370 MPa, and increasing by 18% compared with extruded AZ91 alloys, but the tensile strength of extruded AZ91-X alloys is 320 MPa, just increasing by 2% compared with extruded AZ91 alloys. Through high-temperature tensile test, tensile strength and yield strength of extruded AZ91-X alloys are higher than extruded peak-aged AZ91-X alloys, but elongation is relatively low.2. Replacing elements of WE43 alloys. In order to manufacture Mg-4Sm-3Nd-Zr alloys, Using low-cost element Sm replaces the relatively high price element Y in WE43 alloys. In addition, in order to further optimize magnesium alloys, adding a small amount of elements Gd and Zn on the base of Mg-4Sm-3Nd-Zr alloys, and studying the effect on microstructure and high temperature mechanical properties of as-cast and peak-aged magnesium alloys.The experimental results show that: mechanical properties of as-cast and peak-aged Mg-4Sm-3Nd-1Zr alloys which just using low-cost element Sm replaces element Y of WE43 alloys is not as good as WE43 alloys. Aging strengthening effect will increase when adding a small amount of elements Gd, Zn to the Mg-4Sm-3Nd-1Zr. Through 300℃ high temperature tensile test, tensile strength and yield strength of peak-aged Mg-4Sm-3Nd-1Gd-1Zn-1Zr alloys are 223 MPa and 148 MPa respectively, which are higher than WE43 magnesium alloy, and showing excellent heat resistance.