The Effect Of Ca Addition On The Microstructure And Mechanical Properties Of AZ Magnesium Alloys

The improvement of people's living standard and the enhancement of environmental protection consciousness promote the production of industrial materials to trend to light weight, high quality, low carbon. Magnesium alloy with the series of the advantages such as low density in the industrial field has been Greatly sought after by people.The Mg-Al-Zn magnesium alloy as AZ91, AZ63 and Mg-Al-RE alloy that adding RE elements to improve heat resistance were commonly used. In this paper, tested alloys were based on the cast Mg-6Al-5Zn-5Gd alloy and deforming Mg-6Al-1Zn-1Nd alloys, adding different contents of Ca. It was studied the Ca addition on the micro-structure and mechanical properties of the alloys. The results can provide experimental and theoretical basis for the development of low cost, heat resistant, high Ca and high strength magnesium alloys for automotive and other industrial fields. The result shows that:The micro-structure of as cast Mg-6Al-5Zn-xCa-5Gd alloy is mainly composed of ?-Mg phase, ?-Mg25(Al,Zn)37.5 phase, granular Al2 Gd and the block CaZn5 phase in the grain boundary and dendrite boundary. With the increase of Ca content, the second phase of the network distribution along the grain boundary in the tissue is gradually refined, and the distribution of the second phase is intermittently distributed. After T6 treatment, the age-hardening of alloys reach the peak at 12 h. Then the hardness tends towards stability after slightly decrease, which shows that the alloy has significant thermal stability.Fracture analysis shows that with the increase of Ca, fracture mechanism of the alloys transforms from brittle to ductile. With the Ca content of 6%, dimples can be observed obviously. After the T6 treatment, the dimples increase and the size of them are uniform. The mechanical properties of the Mg-6Al-5Zn-6Ca-5Gd alloy by solid solution treatment at 390?/8h and aging treatment at 200?/12 h were optimal.Extrusion can effectively refine grains. The Extruded Mg-6Al-1Zn-1Ndalloy was composed of ?-Mg matrix, ?-Mg17Al12 phase and Al2 Nd phase. With the increase of Ca content, the new phase Al2 Ca phase appeared. The grain size of the alloy decreases gradually with the increase of Ca content. The hardness increased primarily and then decreased after aging, then leveled off. With the increase of aging time, the solubility of Al atoms in Mg matrix decreased, and the precipitates gradually increased. After aging treatment, the number of fracture toughness nest increase. The strength and elongation of the alloy without Ca are relatively low. Due to the new particle phase Al2 Ca continuous precipitates, the alloy with 2%Ca has higher aging strengthening effect, and with higher tensile strength and yield strength, 299 MPa and 269 MPa,respectively. The elongation of alloy with 2%Ca was 21.6%. With 3%Ca content, the tensile strength and yield strength of the alloy decreased to 276 MPa and 247 MPa, and the elongation was 19.5%.