Hook is a typical defect of lap joint. It can induce stress concentration and is detrimental to joint strength. Thus, hook should be eliminated. In this work, by using the vertical squeezing force of the plastic material near the lap interface, we have successfully eliminated the hook by a double-size friction stir welding process. The results show that the double-side welding method can eliminate the hook in a wide parameter range. The rotating speeds ranging from 800 to 2000 rpm can effectively depress the bending of the lap interface, thereby eliminating the hook. The joint shows high strengths after the hook is eliminated. The maximum failure load of 15.195 kN is obtained when using the rotating speed of 1200 rpm. The joints show shear fracture mode when using rotating speed lower than 1200 rpm, and tensile fracture when the rotating speed is higher than 1600 rpm.
Based on the actual working conditions of the ∅880 × 400 horizontal twin-roll caster, the influence of the rolling speed on the flow field and solidification welding line of AZ31 magnesium alloy in the roll casting area is analyzed by finite element simulation. The results show that the molten metal’s convective heat transfer efficiency is improved by two vortexes (upper and lower) in the roll casting area. When the rolling speed increases, the solidification welding line gradually approaches the outlet. And the flow velocity difference between the middle and the edge of the roll casting area gradually increases, resulting in the continuous increase of the position difference L of the characteristic solidification welding points K and K″ in the rolling direction, which increases the probability of edge cracking of the roll casting strip of magnesium alloy. In order to improve the production efficiency of the roll casting strip of magnesium alloy, it is suggested that the rolling speed should be controlled within the range of 3 4.2 m/min.
Taking the new and old P92 pipes as the object,the rod samples of fine grain heat affected zone(FGHAZ)was prepared by using rapid heat treatment process.The microstructure and properties of the two FGHAZ samples were compared through observation by SEM,TEM,microhardness and creep tests,and the effect of the pipe original state on the microstructure and mechanical properties of FGHAZ of P92 steel was revealed.The results show that compared with that of the FGHAZ of new P92 pipe,the dislocation density of the FGHAZ of old P92 pipe is lower,the size of the precipitates is bigger,which decreases the hardness and creep resistance.During creep test,the FGHAZ of the old P92 pipe has higher precipitating tendency of Laves phase,which promotes the formation of creep void,accelerates the creep fracture and shortens the creep rupture life.
To address the problems such as abnormal wear and the friction layer falling off caused by insufficient adhesion stability of clutch friction pairs formed by traditional sintering and pressing, the laser cladding process manufacturing method was used to prepare the cladding layer of the copper-based powder metallurgy friction materials by using Laserline LDF 6000–100 semiconductor laser, and the prepared friction pairs were tested and analyzed by SEM in this paper. The numerical model of the friction torque of the wet clutch was established, and the friction performance and wear tests were carried out using MM-3000 performance test machine. The friction characteristics of the wet clutch prepared by the laser cladding process were investigated under typical operating conditions. The results show that the accuracy of the numerical model is verified by the experiments; The friction layer prepared by laser cladding technology has compact structure, without obvious crack defects, and has good wear resistance. Compared with the traditional sintering and pressing technology, the wear rate of the friction pairs is reduced by 59.76%; The maximum slipping friction work under different engagement pressures increases with the increase of rotating speed; The friction torque can rapidly reach the maximum value after the clutch is fully engaged, and the equivalent friction coefficient also reaches the extreme value correspondingly at this time.
In this work, refill friction stir spot welding (RFSSW) is innovatively applied to butt weld 6082 Al alloys. The effect of the refilling time on the microstructure and properties of the welded joints was studied. The results show that for the 6082 Al alloy with a thickness of 2 mm, a tool plunge depth of 1.6 mm can successfully avoid the incomplete bonding at the joint bottom. Cracks, formed by insufficient bonding, appear at the tool retraction paths when using the short refilling times of 3 s and 4 s. A prolonged refilling time of 5 s can eliminate the crack due to sufficient diffusion time. The pin affected zone (PAZ) has coarser grains than the sleeve affected zone (SAZ) due to the insufficient tool stirring action. Prolonged refilling time results in coarser grains, lower hardness and higher tensile strength of the joints. The maximum tensile strength of 262.2 MPa is obtained when the refilling time of 5 s is used, and the joint fails at the heat affected zone (HAZ) under such a condition.
