A Study On Mg Melt Continuous Non-flux Purification Theory And Key Techniques

Currently,Mg and Mg alloy melt preparation remains its traditional flux patch purification followed by gas protected melt settlement.Besides the heavily pollutive exhausts and melt contamination,the use of chloride salt leads to the generation of gases corrosive to workshop and equipments.With the continuous growth of Mg industry,solving the quality,environment protection and energy consumption problems in flux based melt preparation process becomes more and more prominent.Naturely,a lot of attention was paid to development of a non-flux method,i.e.,to purify melt under gas protective via integral use of "inert gas + filtration + settlement" purification mechanism.However,due to great property difference of melt contaminants,the rapid degrading filtration efficiency and high filter cost,no mature non-flux refining method is developed for industrial use.In order to solve the problems inherited in non-flux purification,a comprehensive approach is proposed in present study to achieve continuous and effective melt purification,i.e.: A.developing a novel filtering method to realize a continuous and low cost Mg melt filtration;B.developing a sequential contaminants removal process in accordance to the specific properties of contaminants.C.design and construct non-flux Mg melt continuous melting and purification prototype system with integral control mechanism,with which,conducting bulk Magnesium melt non-flux refining to provide samples for further investigation.D.proper use of modern analysis methods to characterize the samples in terms of inclusion geometry and related purification quality.The achievements and conclusions are specified as follows.1.Processing Research and Development“Inclusions suspending in Mg melt tend to agglomerate and settle” was observed and a unique "Mg melt self-clean filtering with reusable steel filter” is developed to provide Mg melt low cost and continuous filtration.Based on in-depth study on the properties of the melt contaminants and the performance of unit melt non-flux purification techniques,a novel continuous non-flux purification process was put forward,which is characterized by its sequentially use of unit purifying mechanisms of “gas refining,inertia separation,self-clean filtration,settlement,dosed pouring" to form “Mg melt non-flux continuous melting and purifying process”.2.Prototype equipment design and constructionAccording to the process principle,a unique "Mg non-flux continuous melting and purifying system" was designed and constructed.At meantime,a PLC integrated control system based on "fuzzy control + PID control" was developed to realize monitoring and control of the melt preparation and supply process as a whole.Compared with the traditional fluxed Mg melting and purification facility,the non-flux one needs less install and operation space,stable,easy to use and maintain,besides its green and continuity in nature.3.Experimental investigation with prototype equipment1)Using a prototype to conduct smelting and refining experiments on ZM6 magnesium alloys,the results show that the melting and protection effect of the developed equipment is stable,and the melt quality does not deteriorate as the smelting time is prolonged.The impurity removal efficiency of the refining system is stable,and is independent of the refining rate within the assessment range.2)When magnesium alloy reclaimed ingots are produced by the non-flux refining process,the yield of cold-house die-casting waste magnesium is 93%~96%,and the yield of hot-chamber block magnesium waste is 88%~92%.The recycled ingot contains more inclusions of smaller size,and there are no abnormally large inclusions.3)Compared with commercial magnesium alloy ingots,the 100% scrap recycled ingots by the non-flux refining process comply with relevant international and Chinese standards for Mg die casting ingots;the recycled ingots have lower corrosion rate and total amount in the acid aqueous solution,and have more excellent corrosion resistance.4)Due to lower processing cost and high reclaiming rate,the processing cost of the recycled ingot is about 1400~3000 Yuan RMB per ton,beside the eliminated logistic cost and potential danger.Compared with the current market price of 5000 ~ 6000 Yuan RMB for recycling of 1 ton scrap into 1 ton ingot,the scrap fluxless continuous recycling technique possesses very attractive technical and economic significance.