Dissertation
Dissertation > Industrial Technology > Metallurgy and Metal Craft > Casting > Special Casting > Other special casting

Microstructure Evolution of Semi-solid A2017 Alloy Prepared by SCR Process and Extending Forming

Author WangShunCheng
Tutor WenJingLin
School Northeastern University
Course Materials Processing Engineering
Keywords Semi-solid metal Shearing/cooling roll process Extruding extending forming Finite element simulation Thixorolling Microstructure evolution Aluminum
CLC TG249.9
Type PhD thesis
Year 2006
Downloads 244
Quotes 3
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A new processing technology-Shearing/Cooling Roll (SCR) was developed to efficiently continuous preparation of semi-solid metallic slurry in the present work. Round and flat bars were produced by a continuous extending extrusion process using an extending die in this SCR technology, which can prepare and form the semi-solid metallic slurry continuously. Main results are achieved as follows:(1) A SCR testing machine was designed. Semi-solid metallic slurry of A2017 alloy was prepared using SCR technology, then semi-solid billets were produced by SCR rheocasting. The effect of SCR processing parameters on the microstructures was investigated, the rheocasting parameters were optimized. It is found that the microstructures of semi-solid billets transform gradually from coarse dendrites or rosette grains into fine homogenous distributed equiaxed grains as the pouring temperatures decreases or roll-shoe gap reduces. When the pouring temperature is 760-780℃ and the roll-shoe gap height is 4-6mm, billets having fine exquixed and rosette grains, fewer cast defects and better surface can be obtained.(2) Through observation of microstructure evolution of semi-solid A2017 alloy during SCR process, it is thought that dynamic shearing can be realized during preparation which promotes microstructure evolution from dynamic nucleation to broken dendrites to spheroidized grains. The melt firstly nucleates at the surface of working rolls and shoes and grow as dendrites. At the effect of shearing and stirring force, dendrites are fall off, some dendrites grow into rosette grains, then form fine exquixed grains, and spherical grains can be obtained by shearing friction finally.(3) It is first time to use three-dimension finite element method to simulate the thermal-fluid multiple field during semi-solid continuous extending extrusion process. A calculation model was built, the boundary condition of the calculation model and

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