| Magnesium/aluminum alloys have the advantages of low density,high specific strength,and abundant inventory,and are widely used in industries such as electronic equipment,automobiles,and ships.Magnesium alloys and aluminum alloys have a wide range of applications,and the joining technology of the two materials has become a hot research direction.As a new type of solid-phase connection technology,friction stir welding can achieve high-quality connection of magnesium-aluminum alloys.In this paper,5083 aluminum alloy and AZ31 magnesium alloy with a thickness of2.5mm are selected as the research base materials,and the dissimilar metal friction stir welding of magnesium-aluminum hetero-alloy is carried out by selecting different welding process parameters.The mechanical properties,microstructure and phase composition of welded joints were studied using universal tensile strength tester,microhardness tester,metallographic microscope,scanning electron microscope(SEM)and Xray diffraction(XRD),and the welding process parameters were obtained.And the relationship between mechanical properties.The main research conclusions are as follows:(1)Welding parameters have a great influence on the appearance of welded joints,and suitable parameters can obtain joints with good appearance.Joints with lower heat input parameters will have defects such as peeling and grooves;joints with higher heat input parameters will have defects such as flashing and rough weld surface.(2)The overall tensile strength of the joint will increase with the increase of the rotation speed,but when the rotation speed exceeds 950r/min,the tensile strength will decrease;the joint tensile strength will decrease with the increase of the forward speed.The maximum tensile strength is 168 MPa at a rotation speed of 950r/min and a forward speed of 50mm/min.(3)The microhardness of the joint will increase with the increase of the rotation speed,but after 950r/min,the hardness will decrease;the microhardness of the joint will decrease with the increase of the forward speed.And all welded joints have weak connections at the roots.The lowest microhardness value is at the center line of the weld.The hardness of the weld nugget zone is higher than that of the base metal zone.The hardness of the heat-mechanical affected zone is the highest,and the hardness of the heataffected zone is the lowest.(4)The grains in the weld nugget area become fine and uniform after dynamic recovery and recrystallization,and with the increase of rotation speed and forward speed,the grains in the weld nugget area are smaller and more evenly distributed;part of the grains in the heat-mechanical affected zone Being elongated and bent,the grains of the heat-affected zone become coarser.The thickness of the mixed layer in the transition zone of the magnesium-aluminum interface becomes narrower with the increase of the rotation speed and the forward speed.(5)As the rotation speed increases,the fracture of the welded joint gradually changes from brittle fracture to ductile fracture.Tunnel defects are found at the 850-50 joint fracture;the joint fracture evolves from a plastic fracture to a brittle fracture with the increase of the advancing speed.A hole defect was abnormally appeared at the fracture of the 950-20 joint,and a tunnel defect was found at the fracture of the 950-60 joint.The fracture surface of the 950-50 joint is relatively flat,and there are no redundant welding defects.(6)X-ray diffraction analysis of the welded joints with parameters of 850-40,950-50 and 950-40 showed that the joint joints contained two high-brittle phase compounds,Al3Mg2 and Al12Mg17,in addition to Mg and Al. |
PDF Full Text Request