Study On Microstructure And Properties Of Mg-Gd-Y-Ca-Zr Alloys

Rare earth magnesium alloys has received wide attention due to their good mechanical properties at room and high temperature, which is becoming a hot spot of research in recent years. But rare earth metals cannot be widely applied because of the price is generally expensive. Ca is one of the alkaline earth elements, and its melting point is low, density is similar to Mg, and costs low. Therefore, on the basis of ensure mechanical properties, Ca is added to completely or partly replace rare earth elements in magnesium alloys to reduce the economic cost. Thus the development of new magnesium alloy containing Ca, will become an important research direction.This paper is based on the Mg-5Gd-3Y-0.5Zr alloy which Ca element is added as the proportion 0.3 wt %, 0.6 wt %, 0.9 wt % and 1.2 wt %, and the microstructure, mechanical properties and corrosion resistance of the alloy were studied.Results show that the microstructure of Mg-Gd-Y-Ca-Zr alloy with different Ca both casted and solution-ageing are formed by α-Mg matrix, Mg2 Ca, Mg5 Gd and Mg24Y5 phases.Grain of magnesium alloy is refined along with the increase of Ca, but it can also lead to the second phase in the alloy increased. The second phase has been distributed in continuous mesh on the grain boundary, when the content of Ca is 1.2wt% in the as cast alloy, and it also partially cover the grain boundary, that make the grain boundary contour is not very clear.After solid solution and ageing treatment, as the increase of Ca content, the tensile strength of four kinds of experimental alloys are increased first and then decreased at the same temperature, which shows the best mechanical properties in Mg-5Gd-3Y-0.6Ca-0.5Zr alloy. The tensile strength of four experimental alloy firstly increase and then decrease with the increase of temperature when the composition of the alloy is determined. The elongation of alloys decreases with the increase of Ca content, which all belong to brittle fracture. Compared with the research of Mg-5Gd-3Y-0.5Zr matrix alloy the tensile strength of alloy with Ca contained are obviously improved, either at room temperature or high temperature. The tensile strength of Mg-5Gd-3Y-0.6Ca-0.5Zr reached 230.305 MPa at room temperature, which is 20 MPa higher than Mg-5Gd-3Y-0.5Zr matrix alloy.The high temperature creep resistance performance of Mg-5Gd-3Y-0.6Ca-0.5Zr alloy is well. When the temperature ranges from 200 to 300℃ ℃, and the stress ranges from 50 MPa to 70 MPa, the creep stress index value is 1.11-2.92, and the creep activation has a value of 147.3-172.7 k J/mol, we concluded that the creep mechanism is mainly diffusion control mechanism transform to grain boundary sliding and dislocation slip control mechanism.The corrosion behavior of four experimental alloys in different concentration of Na Cl corrosive liquid concentration(0.5%, 2.0%, 3.5%) at room temperature were studied. Results show, with the increase of Na Cl concentration the corrosion rate of four kinds of experimental alloys increase when the composition of the alloy is certain. And the corrosion resistant of alloy firstly enhances and then weakens with the increase of Ca content, at the same concentration of Na Cl corrosion liquid. Above all, the corrosion rate of Mg-5Gd-3Y-0.6Ca-0.5Zr alloy is smallest, and the corrosion resistance is the best.