Research On Microstructures And Properties Of HMn57-2-2-0.5Alloy Prepared By Electromagnetic Stirring

Wear-resistant brass is an important material to produce automobile. However, thecomplexity of the manufacturing process and poor stability restrict its development.Electromagnetic stirring affects the solidification process. It can refine grain size, homogenizeorganization and ameliorate the distribution, size and shape of the second phase to improve thematerial performance. In this paper we came up with the idea to apply electromagnetic stirring inthe casting process of wear-resistant brass to optimize the alloy solidification structure and toimprove the wear resistance of synchronizer ring. It has a positive effect of synchronizer ring onindustrial production.In this thesis, we focused on wear-resistant brass HMn57-2-2-0.5, while applying differentintensity electromagnetic stirring during casting process to investigate the change of macro andmicro organizational structure. The HMn57-2-2-0.5alloy is consist of matrix β′, a little offlakiness α phase and dispersed Mn₅Si₃、Fe₃Si hard phase. The internal organizational structureof the alloy changes obviously after electromagnetic stirring. Grain size decreases to50%of thesample with0A electromagnetic stirring when applied50A. Thus, it has been refined obliviously.Electromagnetic stirring affects the heat and mass transfer in the solidification, promotes themetal melt composition and temperature homogenization, changes the size, shape anddistribution of second phase, restrains the formation of Fe₃Si phase and increases the content ofMn5_Si₃. Electromagnetic stirring reduces the β�'α phase transformation temperature and theenergy for the hard phase precipitated from the substrate during aging. It is founded that the mostsuitable heat treatment technology is solid solution at750°C for30min and water-cooled, then,aging1h at350°C. After heat treatment, a lot of hard phase Mn5Si3disperse uniformlyprecipitating on the matrix and little of α phase separated out in the grain. thus we get thewear-resistance organization, including matrix β’, hard phase and little of soft phase. Thecoefficient of friction of the material is greatly reduced and the stability is increased. Coefficientof friction and wear mechanism are closely related with the hardness, microstructure, propertiesand friction conditions. In the same friction condition, the finer of the crystal grains, the more uniform of the organization and distribution of the second phase, the better particle roundness,the harder of the material do good to the wear resistance of the materials.This article presents a new idea and method of increasing wear resistance byelectromagnetic stirring technology. It can change the internal organizational structure toenhance its wear resistance and mechanical properties. This is meaningful for the industrialmanufacture of automobile synchronizer ring.