Design And Preparation Of The Multi-Components Microalloying Materials For Aluminum Cladding And Filling

With the rapid development of our country's industry,aluminum welded structures have been extensively used in civil and military fields,such as vehicles,ships,construction,chemical machinery,aerospace and so on,and aluminum welding has also attracted more and more attention.However,there are some problems such as the softening of the welded joints,low welding coefficient and the welding hot breaking when welding aluminium alloys,which severely restricts the application of aluminum welded structures in various fields.Studies have indicated that optimizing the composition of welding wires was a significant method to improve the microstructure and properties of the welded joints in the condition of unchanging the base metal and welding process.Based on this,the compositions of microalloying ER4043,ER5183 and ER5356 welding wires were designed by changing the contents of main alloying elements and adding microelements such as Sc and Zr.Butt welding and surfacing to the aluminum base metals were carried out with microalloying 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 welded joints and surfacing layers were studied by optical microscopy,X-ray diffraction,hardness testing,tensile mechanical properties testing,scanning electron microscope and transmission electron microscopy.Then the action mechanism of each alloying element and heat treatment was investigated.As a result,the ideal alloying compositions of microalloying ER4043,ER5183 and ER5356 welding wires were developed,which resulted in improving the strength of welded joints and wear resistance properties of surfacing layers obviously.At first,based on the standard composition of ER4043 welding wire,effects of the main alloying element Si,microelements Sr and Mg,and heat treatment process after welding on the microstructures and properties of surfacing layers and welded joints were studied,and the optimal alloying composition of microalloying ER4043 welding wire(Al-5.9Si-0.06Sr-0.3Mg(wt.%))and reasonable heat treatment process after welding(540?/4h solid solution+170?/12h aging)were obtained.Then the compositions of microalloying ER5183 welding wires were designed by changing the content of main alloying element Mg and adding trace Sc,Zr,Er,Ag,and Ce to the welding wires based on the standard composition.Effects of each alloying element and microalloying method on microstructures and mechanical properties of welded joints were investigated,and the optimal alloying composition of microalloying ER5183 welding wire(Al-4.7Mg-0.8Mn-0.1Ti-0.1Sc-0.2Zr(wt.%))was acquired.Compared with the traditional ER5183 welding wire,the tensile strength and yield strength of the welded joint with the microalloying ER5183 welding wire increased by 16.6%and 24.0%respectively.Besides,the differences of microstructures and properties of welded joints with the welding wires between ER5356 and ER5183 were studied.It can be observed that there was little obvious difference of the microstructures of welded joints with ER5356 and ER5183 welding wires,but the strength of the welded joint with ER5356 welding wire was less than ER5183,but the plasticity on the contrary.Additionally,the effects of Sc,Zr and Er microalloying on microstructures and properties of welded joints with the ER5356 welding wire were the same as ER5183.In this thesis,the optimal microalloying ER4043,ER5183 and ER5356 welding wires were developed successfully.Microalloying ER4043 welding wires could be used to weld 6061 aluminum alloy sheets by butt welding and surfacing,and both the microstructures and properties of the welded joints and wear resistance properties of the surfacing layers were excellent.Besides,microalloying ER5183 and ER5356 welding wires could be used to weld 7A52 aluminum alloy sheets by butt welding,and a good combination of strength and plasticity of the welded joints was obtained.The strength of the welded joint with the microalloying ER5183 welding wire achieved a maximum with general plasticity,while the welded joint with the microalloying ER5356 welding wire showed remarkable plasticity,but the strength was slightly less than ER5183.