Study On The Process And Mechanism Of The Near Net Shape Casting Of Wrought Magnesium Alloys By Self-inoculation Method

Compared to casting magnesium alloys, wrought magnesium alloys have used inautomotive, aircraft, 3C, et al, due to its higher properties, for example:strengh,elongtation and good corrosion resistance and fatigue properties. wrought magnesiumalloys adopted high-cost long process to achieve the plastic forming process. So thenear net shape casting of wrought magnesium alloys, which is of very attractiveprospect, can provide complex parts with high strength, high-ductility and low cost.In this thesis, self-inoculation methods is proposed in this project, whichself-inoculator (same composition to that of the alloy melt) is introduced into themelt,and then the melt is poured into a special cooling tank with multi-stream mixingfor further inoculation. By controlling the alloy melt temperature and the localsuper-cooling so that it has a large number of nuclei and ensure the primary phase inthe melt not to remelt. Subsequently, the melt flows through the multi-stream mixedcooling tank. The local super-cooling, flow scouring and mixing result in a smallcritical radius of nuclei for grain growth, enhancing self-inoculation effect, andpromoting grain multiplication,inhibiting grain growth. Finally, the solid-liquid mixedslurry with a non-dendritic primary phase will be obtained. By means of calculationand experiment, the effects of the alloy composition and reaction conditions on theformation of the primary phase during self-inoculation casting. The effect of meltprocessing temperatures on AZ61and ZK61 wrought magnesium alloys semi-solidslurry prepared by self-inoculation method. The effect of structure and angles ofcooling tanks and addition amount of the self-inoculator on AZ61 wrought magnesiumalloy semi-solid slurry prepared by self- inoculation method. The results indicate that:1. Through thermodynamics calculate by Pandat, results shows AZ61 and ZK61wrought magnesium alloys are suitable for semi-solid forming.2. Compared with traditional casting, AZ61 and ZK61 wrought magnesium alloyscasted by self-inoculation method. The dendrites is decreased, the microstructureshowed near-spherical grains,equiaxed grains and less dendrites. ZK61 wroughtmagnesium alloys casted by SIM decreased the dendrites, showing a large number ofnear-spherical grains and multilateral crystal shape.3. The most appropriate melt treatment temperature is 700℃on AZ61 wroughtmagnesium alloy solidified by SIM, which average grain size is 39.8μm. And the most appropriate melt treatment temperature is 725℃on AZ61 wrought magnesium alloy,which average grain size is 22.0μm. Up the melt treatment temperature, the dendritesis increasing and average grain size become bigger in microstructure when the melttreatment temperature is higher. The dendrites is decreasing and spherical grain isincreasing when the melt treatment temperature is lower, the particle size of primarymg phase distribute uniformly in matrix.4. SIM is the best pouring method for AZ61 wrought magnesium alloy that wasprepared. The suitable condition can increase effective nucleation rate and obtain highquality semi-solid slurry, which requires the parameters match angle(45°)of themulti-stream mixed cooling tank and addition of the self-inoculants(5%).5. In the SIM process, the self-inoculator as internal chill can increase the rate ofthe melt nucleation; the multi-stream mixing cooling channel promoting grainmultiplication, inhibiting grain growth. the solid-liquid mixed slurry with anon-dendritic primary phase will be obtained.