Research On Corrosion Resistance Of Mg-Zn-Al-Sn-Mn Alloy Extrusion Profiles

With the rapid development of the economy and society,the problem of energy shortage and environmental degradation is becoming more and more prominent,and the low carbon transformation and upgrading of the manufacturing industry is imminent.As the "21st-century green engineering materials",magnesium alloy has the outstanding advantages of lightweight,high strength,and easy recycling,and has a broad application prospect in the fields of aerospace,rail transportation and automotive.The poor corrosion resistance of magnesium alloy is one of the main reasons to limit its large-scale application.Through the plastic forming process and heat treatment,the microstructure of magnesium alloy can be refined and the corrosion resistance of magnesium alloy can be improved.An important processing method of magnesium alloy profiles is extrusion,three-direction compressive stress to make the billet plastic deformation,to achieve the purpose of refining the grain structure and improving the properties of the profile.The Mg-Zn-Al-Sn-Mn alloy has excellent alloying conditions,creating the preconditions for the improvement of the corrosion resistance of magnesium alloys,but there are few studies on the extrusion and subsequent heat treatment of this alloy,and the evolution of the microstructure and its influence on the corrosion resistance have not been clarified.It is difficult to provide theoretical support for the practical production of Mg-Zn-Al-Sn-Mn alloy.In view of the above problems,this paper takes Mg-6Zn-5Al-3Sn-0.4Mn(ZATM6530)magnesium alloy as the research object and investigates the influence of extrusion temperature and extrusion speed on the microstructure and corrosion resistance of the profile through extrusion experiments;the solution and aging heat treatment of the extruded profile are carried out to study the influence of the solution and aging system on the microstructure and corrosion resistance of the profile.To further improve the corrosion resistance of ZATM6530 magnesium alloy,Al coatings with long-lasting corrosion protection were prepared by cold spraying technology and the effect of cold spraying process parameters was investigated.This study provides theoretical guidance for the extrusion and heat treatment process of Mg-Zn-Al-Sn-Mn alloy and provides new ideas for regulating the corrosion resistance of magnesium alloy,which has important theoretical significance and engineering application value.The main research contents and conclusions of this paper are listed as follows:(1)ZATM6530 magnesium alloy was studied and hot extruded at different extrusion speeds and temperatures.The microstructure and corrosion resistance of the extruded profiles were systematically tested and characterized.The results show that higher extrusion speeds lead to the production of more second-phase particles,an increase in the proportion of recrystallized grains,and a weaker basal texture.In addition,the higher extrusion temperature increases the number of second-phase particles,grain size,and the degree of recrystallization,while decreasing the basal texture strength.Grain refinement leads to much higher corrosion resistance,but as the number of fine and dispersed second-phase particles increases,corrosion resistance becomes worse.(2)For ZATM6530 magnesium alloy extrusion profile,the solution and aging heat treatment experiments with different temperatures and time were carried out to optimize the solid solution process parameters of the profile,and the effect of the solution and aging process on the microstructure and corrosion resistance of the profile was studied.The proposed solution process for ZATM6530 magnesium alloy profile is 400℃ for 2 h.After the solid solution treatment,the average grain size of the profile increased significantly,most of the second phase particles solid solved into the matrix,and the corrosion resistance was improved.The shape,quantity,and distribution of the precipitated phases during the aging of the profile vary considerably depending on the aging time.In the under-aged state,the number of precipitated phases is small;the number of precipitated phases in peak aging is significantly increased and cross-distributed along with specific directions.in the over-aged state,the number of precipitated phases decreases significantly,but the size rises slightly.After analysis,the main precipitated phases during aging are the β1’ phase,β2’ phase,and τ-Mg32(Al,Zn)49 phase.The aging precipitation phenomenon will aggravate the micro-galvanic couple corrosion of the matrix and weaken the corrosion resistance of the profile.(3)To meet the demand for long-term protection of magnesium alloy,Al coating was prepared for ZATM6530 magnesium alloy profile by cold spraying technology,and the effect of cold spraying working gas temperature and pressure on the denseness,thickness,and corrosion resistance of the coating was investigated.It was found that as the working gas temperature increased during the cold spraying process,the average porosity of Al coatings decreased due to the decrease in the critical velocity of the particles,which increased the deposition efficiency.As the working gas pressure increases,the higher gas pressure increases the mechanical bite of the Al coating and enhances the "compaction" effect,with a consequent decrease in the average porosity of the Al coating.The densities of Al coatings are positively correlated with the corrosion resistance.It is noteworthy that the generated corrosion products will collect in the pores or cracks of the coatings,blocking the transmission of corrosion and thus enhancing the corrosion resistance of Al coatings.