Study On The Technology And Application Of Solidification Microstructure Of Semi-solid A356 Aluminum Alloy By Trace Rare Earth Refining

With the clear recognition to the status of RE resource of our country and the deeper research on rare earth,and the level of modification technology were obviously improved at home and abroad,the optimal addition of RE modification has gradually ?micro-addition? development.This paper takes hypoeutectic Al-Si alloy A356,which is widely used in semi-solid metal forming,as study object,adding a single or multiple of rare earth elements respectively to find the optimal content of rare earth,and reveal the refining behavior and changing regulations of the solidification structure of Semi-solid aluminum silicon alloy by Aluminum-rare earth eutectic reaction.Based on the above study,the ideal process was gotten by changing the pouring temperature,electromagnetic stirring frequency and stirring time,for reduce the addition amount of RE to achieve the purpose of micro-addition of RE content.The semisolid slurry of A356 alloy was prepared by electromagnetic stirring technology,which was grain-refined by rare earth La,the influences of La and the fractal characterization of morphology of semisolid primary phase in A356 alloy was studied.The results showed that the morphology of primary phase in semisolid A356 alloy was effectively improved at the suitable addition of La,and the optimal content of La was 0.40%(quality score)in this experiment.At the same time,the morphology of primary phase in semisolid A356-La alloy by electromagnetic stirring was better than not stirring.In addition,the actual solidification organization has fractal characteristics,it was feasible to description and analysis the change regularity and even the formation mechanism of the morphology of primary phase in semi-solid aluminum alloy by the principle of fractal geometry.The morphology of primary phase in semisolid A356 alloy by the different process parameters had different fractal dimension.The fractal dimension of the semisolid primary phase gradually became smaller with its morphology changed from dendritic to granular or globular.Based on the above study,the semisolid slurry of A356 alloy was prepared at different pouring temperature and electromagnetic stirring,the morphology of primary phase and mechanical properties of the semisolid A356 alloy were researched under the pouring temperature ?electromagnetic stirring frequency and treated time with the trace RE.The results showed that,it was feasible to reduce the addition amount of RE by optimizing the semisolid slurry process conditions.The suitable preparing parameters were obtained by the experiment,in which the pouring temperature was 630 ?,the frequency of electromagnetic stirring was 30 Hz,and the stirring treated time was 8s.At this point,when the content of La addition was 0.3%,the modification effects of the semisolid A356 alloy was indistinguishable with the conventional addition amount of 0.4% La in low superheat pouring,and their mechanical properties were close to each other.In the condition of above-mentioned the best Micro-addition of RE process,the semisolid slurry of A356 alloy was prepared,which was grain-refined by Al-Ce,Al-Y master alloy and mixed rare-earth containing La,Ce and Y with different ratios,the influences of different micro-addition rare earth on the morphology of semisolid primary phase in A356 alloy by the best micro-addition of RE process was studied.Results show that the most proper addition of multiple RE is 0.2 % La+0.3 % Ce+0.4 % Y under the best micro-addition of RE process,thus the average equal-area circle diameter and the average shape factor of semisolid A356 alloy are 81.10?m and 0.78,respectively.It was feasible to further reduce the addition amount of RE by optimizing the semisolid slurry process conditions and mixed rare-earth.