Effects Of Cu And/or Zn Addition On The Microstructure,Mechanical And Corrosion Behaviors Of Mg

Magnesium alloy is the lightest commercial metal material.Owing to its excellent properties,it has been widely used in the field of automobile industry,electronic products,aerospace and so on.However,the strength and plasticity of pure Mg and widely used Mg alloys are relatively low.Grain refinement,as an important method to improve the strength,ductility and plasticity of Mg alloys at the same time,has been a research hotspot for years.Owing to their reasonable growth restriction factors?GRF?,Cu and Zn could be effective grain refining elements for Mg.However,the rencent researches about Cu and Zn addition in Mg mainly focused on the aging behavior of Mg-Zn-Cu alloys and no investigation on the mechanism of the grain refinement after Cu and Zn addition was presented.In this paper,the different Mg alloys before and after Cu and/or Zn addition were used as the experimental material.The effects of Cu and/or Zn addition on the microstructures and grain sizes of Mg alloys were firstly discussed and the mechanism of grain refinement after Cu and/or Zn addition was explained.What'more,the phase compositions of different Mg alloys before and after Cu and/or Zn addition were revealed.Finally,the effects of Cu and/or Zn addition on mechanical and corrosion behaviors of Mg alloys were investigated.The main conclusions are as follows:?1?After Zn,Cu and Cu+Zn addition in the pure Mg,the grain sizes of the alloys decreased from 1270?m?pure Mg?to 470?m,120?m and 85?m,respectively and the crystal morphology changed from columnar grain to equiaxed grain.The Cu and Zn addition had the best grain refinement effect on pure Mg,then the Cu addition followed and the Zn addition was the worst?2?After Zn addition,Mg-3Zn alloy was composed of?-Mg and MgZn phases.The secondary phases were mainly in the morphology of tiny particles.After Cu addition,Mg-5Cu alloy was composed of?-Mg and CuMg₂ phases.The secondary phases were mainly in the morphology of discontinuous herringbone structure.After Cu and Zn addition,Mg-5Cu-3Zn alloy was composed of?-Mg,CuMg₂ and CuMgZn phases.It was found that CuMg2 phases were in the shape of continuous bulk and the CuMgZn phases were in the in the morphology of discontinuous herringbone structure.?3?The grain refinement of Zn addition on pure Mg was mainly due to the effect of solute Zn element.And the mechanism of the grain refinement of Cu addition was the effect of solute Cu element and pinning effect of CuMg2 phases on the grain boundaries of?-Mg.However,after Cu and Zn addition,the grain size was finer than Mg-3Zn and Mg-5Cu alloys.This was mainly due to composite solute effect of Cu and Zn element and stronger pinning effect of the secondary phases.?4?After Zn,Cu and Cu+Zn addition in the pure Mg,the microhardness of the alloys increased from 29HV to 49,56 and 62HV,respectively and the ultimate tensile strength increased from 90.1MPa to 141.5,150.2 and 159.5MPa,respectively.What's more,after Zn addition,the elongation of the alloys increased from 6.1%?pure Mg?to7.9%.However,after Cu and Cu+Zn addition,the elongation of the alloys decreased,at4.7%and 4.6%,respectively.?5?The corrosion resistance of the Mg alloys before and after Cu and/or Zn addition was in the order of Pure Mg>Mg-3Zn>Mg-5Cu-3Zn>Mg-5Cu.The differences in the corrosion resistance of the alloys were mainly related to the factors such as:the content and electric potential of secondary phases,corrosion types,protection of passive film and so on.