Study On Non-uniformity Of 2A14 Aerospace Aluminum Alloy Welding Joints

2A14 aluminum alloy is a forging aluminum alloy that can be heat-treated and strengthened.It is one of the main materials used for carry rocket tanks in China.The safety of the welded joint has become a problem that must be faced in designing and manufacturing.However,the use of variable-polarity TIG welded joint still has serious softening problems.The internal microstructure and mechanical properties of joints are not uniform,and the strength coefficient is low.Therefore,the study of the nonuniformity of 2A14 aluminum alloy TIG welded joints and the method for improving the softening of the joints have great practical significance for improving the manufacturing level in industry.In this work,2A14 aluminum alloy was selected as the object,with the T6 and T651 state,different thickness of the test panel using single-sided single-layer and singlesided double-layer welding method.The microstructure and mechanical properties of joints in different regions of the joints were studied.The grain morphology and size,the distribution of pores,the distribution of the elements and the second phase of the joints were studied in various aspects.The hardness test and static tensile mechanical properties and micro-zone tensile testing,combined with microstructure analysis.The weld zone is consisted of equiaxed dendritic,the grains are coarse with the coarse eutectic precipitates intergranular,and the mechanical properties are poor.In the solid solution zone,the grain has a certain degree of coarseness compared with the base metal,and a supersaturated solid solution is formed after the welding process.After the natural aging,the peak hardness is better than the weld zone.In the overaging zone,the difference between the crystallites and the base metal region is not significant,but the dissolution and coarsening of the precipitates significantly reduce the hardness and lead to softening of the joints..The relationship between the micro-hardness of the microregion and the micro-hardness of the corresponding place was established,and an empirical relationship between the hardness and strength was established.In order to improve the softening problem of the joints,this work added a partial forced cooling device in the welding process to improve the joint strength.The thermocouples were used to collect temperature curves.The cooling device significantly speeds up the cooling rate of the heat affected zone,reducing the peak temperature and the high temperature duration,thereby reducing the softening behavior.Combined with the thermal cycle curve and the classical roughening theory,it was found that the high temperature aging time and the peak temperature are the main factors that promote the coarsening of the precipitate phase.By analyzing different precipitation strengthening models,it was found that the strengthening mechanism of precipitation coarsening would greatly reduce the original effect.