| Friction stir welding(FSW)is a new type of solid phase connection technology,which is widely used in the welding of light alloys.However,the existing friction stir welding machine is often bulky and expensive,which greatly limits the application of friction stir welding.This thesis takes small digital milling machine as the infrastructure,and then designs and manufactures the friction tool,backing plate,fixture and other devices,so it can be transformed into a portable friction stir welding machine with small volume and light weight;Through the exploration of welding process of the thin 1060 aluminum alloy plate,the geometric parameters of the friction tool,tensile testing and microstructure analysis,the welding parameters that are more suitable for the welding of 1060 aluminum alloy sheet by portable friction stir welding machine are obtained,which proves the feasibility of portable friction stir welding machine.In order to expand the application of portable friction stir welding machine,the pre-heat treatment was taken later in welding 6061 aluminum alloys with higher strength.The results are as follows:(1)When using a portable friction stir welding machine to weld 1.4 mm thickness1060 aluminum alloy,it was found that when the shoulder diameter is more than 6 mm,the forward resistance is large,and the welding machine cannot move;when using a 5mm shoulder diameter,it is found that some of the weld surface is smooth and flat,but there are large cavity in the weld cross section.When the spindle speed is 3000 r/min and the welding speed is 300 mm/min,the joint tensile strength reached to the peak value of 73.93 MPa,which is 56.10% of the tensile strength of the base material.(2)In order to improve the welding quality,this thesis compares the performance of the joints of 1.4 mm thickness 1060 aluminum alloy under four different geometric parameters of the friction tool.When the friction tool has a root-diameter of 2 mm and an end-diameter of 1 mm,the welding quality can be good.At the spindle speed of 3000r/min and the welding speed of 300 mm/min,the surface of the weld is smooth and flat,and the tensile strength of the joint is basically equivalent to that of the base material.The hardness value in welded joints were more than that of the base material.(3)In order to expand the application of the portable friction stir welding machine,pre-heat treatment is performed on the 6061 aluminum alloy with a thickness of 1.4 mm,the backing plate is heated by a thermocouple,and then the heat is transferred to the workpiece.The experiment compares the joint performance under three temperature conditions: no preheating,50? preheating,and 100? preheating.The experiment found that when the preheating temperature is 100?,the welding quality is relatively stable,and the average tensile strength of the joint reaches 222 MPa,which is 94% of the tensile strength of the base material.With the increase of the preheating temperature,the smaller the voids appear in the zone,but the larger the grains in the weld nugget area;in the non-preheated state,the hardness value of each area of the welded joint is basically higher than the hardness value of the base material.By contrast,when the preheating temperature is 50? or 100?,the hardness value of each area of the joint is basically lower than that of the base material.The experimental results show that under appropriate welding parameters,the portable friction stir welding machine can weld aluminum alloy sheet,and at the same time,through pre-heat treatment,it can expand its application range and enable it to weld higher strength alloys. |
PDF Full Text Request