Experimental Research On Friction Stir Joining Of AA6061 Box Packaging

In general,laser welding technology is used to package electronic instruments in the protection box in aerospace equipment.Although this technology enjoys a high processing efficiency,however the high reflectivity of aluminum and magnesium materials and the poor quality-consistency limits its yield in industry.As friction stir joining(FSJ)has been widely used in the joining processing of aluminum,magnesium and other materials with significant advantages,this paper carried out the applying of FSJ technology in the packaging process of 6061 aluminum alloy box,and completed the related key technology research.The main work done and achievements attained are following:1.Numerical simulation of temperature field distribution during box packagingA special test equipment was in the packaging joining experiment with appropriated joint form and processing parameter window.After that,the temperature distribution of box packaging under different processing parameters was calculated by using sub-model to increase the calculation accuracy,and compared with the experimental data.The figure shows that there is a significant temperature accumulation effect in the peak temperature of the box packaging process,and the heat source had an opposite asymmetric shape to the straight direction FSJ.The variety of temperature of measuring point is linear with the variety of rotating speed of stirring tool and joining speed.2.Material flow simulation of fillet weld trajectoryAs the pattern of welding trajectory at the corner was with a poor quality,a material flow simulating at this location was done.The material flow visualization at the corner is realized by tracing particles and flow traces.The study found that there was a serious deviation of the material in the advance side of the stirring tool in the corner structure,while a loss of material in the retreat side existing,with stagnant and deposition behind the stirring tool.The above factors leaded the distortion and stratification of the scale pattern at the corner.Under different processing parameters,the increase of rotation speed/ joining speed ratio increases the dynamic viscosity of the material and reduces the driving effect of the stirring tool.Besides,the increase of rotational speed raised the velocity gradient of the medium speed zone of material flow and improved the quality of the joint,while a too high or too low joining speed would decrease the speed gradient,which was bad for the distinctness of the metallographic zone.3.Inspection and analysis of packaging qualityThe residual height deformation and air tightness of the packaged box were measured and analyzed.The experimental results show that the residual height deformation of FSJ was smaller than that of brazed package but larger than that of laser welding.The welding sequence starting at short edge midpoint caused the maximum deformation appearing in the second joining corner.In addition,all the specimens met the existing air tightness standard,some even enjoying an upper as twice as that of standard requirement.The leakage openings were all located at the retreat side of the stirring tool after the first connecting corner,in a shape of narrow tunnel.The direct reason of leakage was the expansion of micro defects in the joint,which was formed by the insufficient filling of material flow during the corner joining.