Continuous Rheo-rolling Of Mg-3Sn-Mn Alloy Under Action Of Roll Shearing

In this paper, according to the Natural Science Foundation of China (No.50974038, No.51034002), continuous rheo-rolling of Mg-3Sn-Mn alloy under action of roll shearing was studied. Self-made test machine was designed and consummated. Experimental parameters have been optimized. The mechanical analysis of the alloy was done during the process of continuous rheo-rolling under action of roll shearing. Microstructures formation mechanisms of Mg-3Sn-Mn alloy were investigated during the process of continuous rheo-rolling under action of roll shearing. Deep rolling and heat treatment of Mg-3Sn-Mn alloy plates which were prepared by continuous rheo-rolling under action of roll shearing were done, and the microstructure and properties was studied after deep rolling and heat treatment. Main work and results are described as follows:(1)A new technology theory of continuous rheo-rolling under action of roll shearing has been proposed. The test machine has been designed. The process conditions of continuous rheo-rolling of Mg-3Sn-Mn alloy under action of roll shearing have been set up.(2) The mathematical model of unit rolling pressure distribution in rectangular groove during continuous rheo-rolling under action of roll shearing was established. The effects of process parameter on unit pressure were analyzed. The smaller the thickness of rheo-rolled plate is, the narrower the width is, the bigger the peak unit rolling pressure is and the larger the average unit rolling pressure is. However, when the plate thickness decreases, the peak unit rolling pressure moves towards the exit while when width decreases, the peak unit rolling pressure moves towards the entrance. The larger the roll radius is, the bigger the peak unit rolling pressure is, the larger the average unit rolling pressure is, and the peak value deviates towards the exit.(3) The effects of process parameter of continuous rheo-rolling under action of roll shearing on microstructure of Mg-3Sn-Mn alloy plate were obtained. Casting temperature varies from690℃to730℃, with the decrease of casting temperature, the width of columnar grain zone near the edge of the product increases, the equiaxed grain zone in the central position decreases, but the primary phases a-Mg increase and are gradually spheroidized in equiaxed grain zone. Roll speed varies from0.052m·s-1to0.087m·s-1, with the decrease of roll speed, the width of columnar grain zone near the edge of the product decreases and the width of equiaxed grain zone in the central position increases. When casting temperature is690℃and roll speed is0.052m·s-1,magnesium alloy profiles have been obtained, the surface and microstructure of the products are excellent.(4) Microstructures formation mechanisms of Mg-3Sn-Mn alloy plate were analyzed during the process of continuous rheo-rolling under action of roll shearing. Heterogeneous nucleation of the alloy occur firstly on the surface of roll-shoe, the cooling rate of the alloy is higher near the surface of roll-shoe and the supercooling degree is bigger, which is favorable to the grains grow in dendrites form. Because of laminar shearing caused by the roll, the preferred orientation of heat dissipation is not obvious, and the solute distribution is homogenous, the grains grow in golobular or equiaxed form. The dendrites are spheroidized under the shearing fracture mechanism of dendritic arms and the blowing-out mechanism of dendritic arms.(5) Through deep rolling and heat treatment of Mg-3Sn-Mn alloy plates produced by continuous rheo-rolling under action of roll shearing, the alloy product with dood properties were obtained. The solution-treated plates of Mg-3Sn-Mn were treated by aging treatment, the second phases precipitate along the grain boundaries firstly, with the extension of aging time, the second phases precipitate within grains. With the increase of aging temperature, the second phases precipitate faster, and the grains get coarse easily. The deep rolling plate after solution treatment at430℃for13h and aging treatment at300℃for12h, its tensile strength can reach over305MPa and as well as elongation over7.8%.