The Influence Of Ti To The Mechanical And Corrosion Resisting Properties Of Casting Zn-Al-Cu-Mn-Mg Alloy

In this thesis alloying element (Ti) is added in casting Zn-Al-Cu-Mn-Mg alloy. Heattreatment and electrochemical corrosion experiments are operated. The influence of Ti to themicrostructure and properties of the alloy is studied. The optimal amount of Ti added inZn-Al-Cu-Mn-Mg alloy is obtained and relational theories are analyzed.The microstructure of casting Zn-Al-Cu-Mn-Mg alloy is coarsening multiphase consistingof nubby and arborescent crystal. Matrix of the alloy contains the phase (η) of enriching Zn andthe phase (α) of enriching Al. Small quantities of Cu and Mn that play important roles in solutionstrengthening dissolve in the matrix. Great masses of Cu and Mn cluster in the grain boundary byforming CuZn5and MnAl6respectively. The minute mass of Mg dissolves in the matrix.Solid solubility degree of Ti in the matrix is quite low, and more Ti forms thehigh-melting-point compound of Al3Ti with Al in the process of the solidification. The tinyparticle of Al3Ti proves to be the heterogeneous crystal nucleus which increases the amount ofcrystal grains, so that plays an important role in fine grain strengthening and enhances themechanical property of the alloy. When the mass fraction of Ti in the alloy is0.10%, there is thewell-proportioned microstructure of fine grains in Zn-Al-Cu-Mn-Mg alloy and tensile strengthincreases to the maximum value of437MPa. When mass fraction of Ti in the alloy is0.15%,Brinell hardness and percentage elongation increase to the maximum values of135HB and1.64%respectively.Heat treatment experiments indicate that, when the mass fraction of Ti in Zn-Al-Cu-Mn-Mgalloy is0.10%, by360℃solution treatment for3h and120℃aging treatment for1h, there is thestable and well-proportioned microstructure of fine grains with the second phase particlesseparating out in the alloy. Fine grain strengthening in matrix interacts with dispersionstrengthening of the second phase particles so that Brinell hardness of the alloy increases to178HB.Corrosion experiments indicate that, in NaCl solution, when the mass fraction of Ti inZn-Al-Cu-Mn-Mg alloy is0.15%, the corrosion processes of the alloy alter and the corrosionproduct of Zn5(OH)8Cl2which plays an important role in protecting matrix is generated. InNaOH solution, Ti in the alloy reduces potential differences among different phases and thedriving force of electrochemical corrosion decreases so that the corrosion resisting property ofthe alloy is enhanced.