Study On Corrosion Characteristics Of Mg-Gd-Ni Alloy Containing LPSO Phase

Magnesium alloy is one of the most promising green mechanical materials in the world,and has been favored by most researchers in recent years.The advantages of magnesium alloys make it a promising future in industrial production.The main characteristics of magnesium alloys are low density,light weight,strong pressure resistance,good shock absorption effect,energy saving and environmental protection.At present,magnesium alloys are widely used in both military and civilian fields,and are mainly used in the military field for aerospace equipment materials.The performance analysis of aerospace electronic equipment,civil aspects mainly include the processing of automotive parts,research on green energy-saving materials.The Mg-Gd-Ni alloy with long period ordered structures（LPSO）phase has the characteristics of high strength and poor corrosion resistance.These performance characteristics are suitable for applications in the field of temporary plugging tools in oil and gas wells.This paper is based on the further study of the magnesium alloy used for temporary plugging tools.Through the systematic analysis and analysis of the corrosion and mechanical properties of Mg-Gd-Ni alloy,it is expected to develop a new type of magnesium alloy for underground temporary plugging tools.In this paper,three kinds of Mg_98.4Gd_1.2Ni_0.4,Mg_97.2Gd_2.1Ni_0.7 and Mg_96.0Gd_3.0Ni_1.0 alloys with the same Gd/Ni atomic ratio but different volume fractions of LPSO phase were prepared by traditional casting method.Scanning electron microscopy（SEM）,X-ray diffractometry（XRD）,transmission electron microscopy（TEM）and electrochemical test systems were used to study the microstructure,mechanical properties and corrosion mechanism of Mg-Gd-Ni alloys containing LPSO phase and the effect of the content of LPSO phase on the mechanical properties and corrosion properties of Mg-Gd-Ni alloy.The main research results are as follows:（1）The Mg-Gd-Ni alloy mainly consists ofα-Mg and LPSO phases.With the increase of Gd and Ni content,the volume fraction of LPSO phase increases continuously,and the LPSO phase changes from discontinuous layer to continuous network and then bulk LPSO phase.With the increase of volume fraction of LPSO phase,the grain size become smaller obviously.（2）There is no Ni in the Mg matrix by analyzing the alloy composition,and it is considered that all of the Ni added in the alloy participates in the formation of the LPSO phase,and Ni promotes the formation of the LPSO phase.（3）The Mg-Gd-Ni alloy undergoes micro-galvanic corrosion.Compared with the Mg matrix,the LPSO phase shows a lower potential.During the corrosion process,the LPSO phase preferentially corrodes as an anode,and then the corrosion path follows the LPSO phase.（4）During the corrosion process of Mg-Gd-Ni,as the corrosion product increases,more micro-couples are formed between the corrosion products,resulting in an increase in the corrosion rate.（5）As the volume fraction of the LPSO phase increases,the grain size of the alloy gradually decreases,and the LPSO phase hinders the slip of the dislocation,so that the strength of the Mg-Gd-Ni alloy increases continuously,and at the same time,with the volume fraction of the LPSO phase increasing,the Mg/LPSO phase interface increases.Then,the stress concentration occurs,and the plasticity of the alloy decreases.（6）With the increase of volume fraction of LPSO phase,the corrosion rate of Mg-Gd-Ni alloy is increasing,the corrosion rate of Mg_98.4Gd_1.2Ni_0.4 is the slowest,followed by Mg_97.2Gd_2.1Ni_0.7,Mg_96.0Gd_3.0Ni_1.0 has the fastest corrosion rate.