| The development of low-carbon environmental materials has become a trend In recent years,and magnesium has been more and more used in the aerospace and national defence industry.But with the characteristics of high chemical activity and oxidizable,it becomes easily to occur corrosion,abrasion and crack on the surface of magnesium alloy equipment,surfacing welding,as a representative of surface cladding technology,could repair the damaged surface of magnesium materials effectively.In general,performance of local part which was repaired can affect the overall performance of the materials,so it’s important to promote the local performance of repaired part.Studies have indicated that optimizing the composition of welding wires and reasonable heat treatment were significant methods to improve the microstructure and properties of the surfacing layers in the condition of unchanging the base metal and welding process.Therefore,based on the wide using of Mg-Al-Zn magnesium alloy(AZ series)welding wires,designing the compositions by changing the contents of main alloying elements and adding microelements such as Y,Gd,and Ce.Surfacing welding was carried out with alloying welding wires,and heat treatment to the surfacing layers was implemented as well.After that,The effects of main alloying elements,microelements and heat treatment process after welding on microstructures and mechanical properties of the surfacing layers were studied.Then the action mechanism of each alloying element and heat treatment was investigated.As a result,the ideal alloying compositions of alloying AZ series magnesium alloy welding wires were developed,which resulted in improving the wear resistance properties and corrosion resistance of surfacing layers obviously.The main contents of this study includes:(1)The effects of main alloying elements such Al,Zn,Mn on microstructures and mechanical properties of the surfacing layers;(2)The effects of heat treatment on microstructures and properties of the surfacing layers;(3)The effects of rare earth elements such as Y,Gd,and Ce on the microstructures and properties of the surfacing layers.The main results are as follows:(1)In the composition of this experiment,β-phase was gradually increased with the increase of Al from 3%to 9%,the hardness was enhanced increasingly too,and the wear resistance was lowest,numeric value is 2.14×10-2 mm3/m;(2)Zn could improve the hardness of Mg matrix due to the effect of solution strengthening,which is in favor of the wear resistance;(3)The effects of adding Mn on microstructures and mechanical properties of the surfacing layers is not obvious.The hardness of alloys with different content of Mn is about 70.0HV.The wear resistance was 2.10×10-2mm3/m under the load of 25N.(4)The reasonable heat treatment could result in a fine-dispersed β-phase,which could preferably protect the matrix and exhibiting a strengthening effect and resisting the wear effects.Under the conditions of this experiment,the reasonable heat treatment process after welding with AZ91wires is:(410℃/12h solid solution+200℃/12h aging);(5)The addition of Y could reduce the size and quantity of β-phase in the a-Mg matrix,which enhanced the alloy strength and hardness and decreased the subsurface metal deformation degree caused by friction,and as a result,improve the wear resistance of welding layers,the hardness changed from 69.0HV to 51.7HV with Y changed from 0%to 2%,and wear resistance decrease from 4.26×10-2 mm3/m to 3.02×10-2 mm3/m,after four days’ soaking corrosion,it turned out that the surfacing alloy with 1%Y shows the best corrosion resistance,average corrosion rate decrase from 2.98 mg·d-1·cm-2 to 0.148 mg·d-1·cm-2 compared with AZ91-0Y.(6)The addition of Gd had improved the wear resistance and corrosion resistance of welding alloys,and the results indicate that the surfacing alloy with 0.5%Y had best wear-resisting property,while the best best corrosion resistance comes to AZ91 with 1%Gd.(7)The surfacing alloy with 1.5%Ce showed fine corrosion resistance and wear resistance,the average corrosion rate is lowest as well as the wear rate.(8)The experimental result of adding three different rare earth elements indicated that the surfacing alloy with 1%Y had best performance of corrosion resistance and the layers with 0.5%Gd showed the best wear resistance,the numerical value had reduced by 95.0%and 35.7%respectively. |
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