The Preparation Of Mg-Gd Master Alloy And Its Impact On The Performance Of AZ91

The pursuit of lightweight and energy saving is the development tendency of the manufacturingindustry in the21st century. The lightest metal magnesium alloys can be used as structuralmaterials, which is known as the green and lightweight structural materials in the21st century,will play an important role in the future. The advantages of magnesium alloys are low density,high specific strength, high specific stiffness, high damping, noise damping, anti-electromagneticradiation, and no pollution during processing and recycling. However, magnesium alloys are easyto burn and to corrosion, which are low strength at high temperatures. Among these alloys, theAZ91is a widely used series.Alloying treatment is one of the main methods to improve the performance of magnesium alloys,which has been proved by theory and practice. During the process, rare earth elements are themain alloying elements of the magnesium alloys. The differences on density and melting pointbetween rare earth elements and magnesium are prone to giving rise to eliguation if rare earthelements are directly added during the smelting, so rare earth elements are firstly made in the formof magnesium master alloys, which are added to the magnesium alloys. There are several methodsfor preparing master alloys，molten salt electrolysis and mix-melting method are the most widelyused methods among them.The AZ91+Gd alloys with different levels of Gd were prepared by AZ91and master alloyswhich produced through molten salt electrolysis and mix-melting method.The organizationalstructures of the master alloys of Mg-Gd and the AZ91+Gd alloys were tested by Metallurgicalmicroscopy, X-ray diffraction and Scanning electron microscopy, We found the differences on theorganizational structure of Mg-Gd master alloy and their effect on the AZ91+Gd alloys;thehardness were tested by hardness tester, the tensile strength and the elongation were tested byElectronic tensile testing machine; the corrosion rates of the alloys were tested by corrosionweight-loss method, and its polarization curves and alternating current impedance were tested byelectrochemical measurement technology.The results showed that: there are differences between organizational structures of master alloysof Mg-Gd prepared by molten salt electrolysis and mix-melting method.The composition ofmaster alloys of Mg-Gd prepared by molten salt electrolysis process is relatively uniform, whichare mainly composed of Mg, Mg5Gd and Gd; the composition of master alloys of Mg-Gd preparedby mix-melting method is composed of Mg and Mg5Gd.Different master alloys of Mg-Gd will result in different effects to the mechanical properties ofAZ91alloys.First, with the increasing of Gd content, the hardness, tensile strength and elongationofAZ91magnesium alloy were increased and when the content of more than2%,all of thosedecreased; the fracture mode is belonged to brittle fracture by means of fracture analysis; thepolarization curves, ac impedance spectroscopy and full erosion corrosion experiment showedthat, the corrosion resistance of the alloy AZ91will be decreased when Gd added is less than1.5%; the corrosion resistance of the alloy AZ91will be increased when the added amount of Gdexceeds1.5%. Secondly,it’s a good choice add Gd to AZ91alloys in form of Mg-Gd master alloy prepared by molten salt electrolysis.The test results of alloys performance are in accord with the analysis of the organizationalstructures, which indicate that the molten salt electrolysis has broad prospects for preparing themaster alloys of Mg-RE; rare earth element Gd can effectively improve the physical and chemicalproperties ofAZ91magnesium alloys.