A Research On ZM6 Magnesium Alloy Melt Fluxless Continuous Preparation Process

Zr containing Mg alloys have many important applications in astronautic and aeronautic light weight structures due to their outstanding properties at elevated temperature.However,Zr has to be blended into Mg alloys by patch addition of Mg-Zr master alloy under force stirring and flux protection in conventional melt preparation process,notorous for its side effects,such as low and instable yielding,tough condition and contamination.Naturely,development of an environmental friendly,high blending efficiency Zr containing Mg alloy melt continuous preparation technique is of great concern from Mg industry.The present study is,therefore,focused on the feasibility of fluxless and continuous ZM6 melt preparation and relevant theoretical issues.To do so,melt purification effectiveness,Zr yielding rate,Zr existence state in melt,size and amount of inclusions and grain refining effect concerned with different zirconium addition methods were investigated by experimental investigations with a fluxless Mg continuous melting and purifying furnace and OM,XRD,SEM,EDS and XRF examination and theoretical analyses.The conclusions are detailed as follows:(1)Free of inclusions with its average size larger than 11?m in samples prepared make evidence that the fluxless continuous purification method can effectively remove large size impurities from melt to achieve satisfactory purity in pouring chamber.(2)It is made evident that Zr in Mg melt exists mainly as suspending partiles that can be largly removed from the melt when subjected to fluxless purification.Consequently,Zr concentration in the prepared melt is less than 0.3wt.% when 1.5wt.% Mg-Zr master alloy is added into charging chamber,and is raised up to 1.1wt.% while the same amount of master alloy is added into pouring chamber.(3)During fluxless melt preparation,continuous addition of Mg-Zr master alloy leads to a high,stable yielding rate and satisfactory melt pourity featured by smaller and less inclusions in prepared melt.(4)During fluxless melt preparation,Zr concentration in the top melt of pouring chamber is lower than that close to the bottom,and the grain size of the casting sample becomes bigger as a direct consequence.This indicates the gravity still plays an role in promoting the segregation of suspending Zr particles under applied stirring intensity.Proper manipulation of the stirring intensity is the key to depress the segregation.(5)With fluxless melt preparation,Zr concentration in melt can be raised up to 1.2wt.% in pouring chamber and the grain size is further reduced accordingly.The average grain sizes of the samples prepared from the top and bottom melt of pouring chamber is 17.69?m and 15.39?m,respectively.