No abstract

This article describes the effect of friction welding conditions and aging treatment on the mechanical properties of type 7075-T6 aluminium alloy (A7075) friction welded joints. A7075 was joined by using a continuous drive friction welding machine with an electromagnetic clutch in order to prevent braking deformation during as rotation speed decreases. That is, it was welded by using the ‘Low Heat Input Friction Welding Method’ (LHI method) developed by the authors, in which heat input is lower than in the conventional method. The maximum joint efficiency at a friction pressure of 30 MPa was approximately 25%, and that at 90 MPa was approximately 64%. These joints were made without forge pressure. The low joint efficiency was due to the existence of non-joined regions at the welded interfaces. However, the welded joint had approximately 82% joint efficiency when the friction time was 0·5 s at a friction pressure of 90 MPa with a forge pressure of 180 MPa. The welded joint softened at the welded interface and its adjacent region. It had approximately 90% joint efficiency after aging for 730 days at room temperature (natural aging). It also had approximately 95% joint efficiency after aging for 48 h at 393 K (120°C), and had no softened region at the welded interface. The heat input of the welded joint with the LHI method could be decreased to approximately 50% of that with the conventional method. The LHI method has several advantages for A7075 friction welding; less heat input than with the conventional method, and light post-weld processing (machining, etc.) because the flash can be minimised.

No abstract

This paper describes the joining phenomena and joint strength of friction welded joints between pure aluminium (P-Al) and low carbon steel friction welds. When the joint was made at a friction pressure of 30 MPa with a friction speed of 27?5 s 21 , the upsetting (deformation) occurred at the P-Al base metal. P-Al transferred to the half radius region of the weld interface on the low carbon steel side, and then it transferred toward the entire weld interface. When the joint was made at a friction time of 0?9 s, i.e. just after the initial peak of the friction torque, it had y93% joint efficiency and fractured on the P-Al side. This joint had no intermetallic compound at the weld interface. Then, the joint efficiency slightly decreased with increasing friction time. The joint had a small amount of intermetallic compound at the peripheral region of the weld interface when it was made at a friction time of 2?0 s. When the joint was made at a friction time of 0?9 s, the joint efficiency decreased with increasing forge pressure, and all joints were fractured at the P-Al side. Although the joint by forge pressure of 90 MPa had hardly softened region, it had y83% joint efficiency. To clarify the fact of decreasing joint efficiency, the tensile strength of the P-Al base metal at room temperature was investigated, and the tensile test was carried out after various compression stresses and temperatures. The tensile strength of the P-Al base metal has decreased with increasing compression stress at any temperature. Hence, the fact that the joint did not achieve 100% joint efficiency was due to the decrease in the tensile strength of the P-Al base metal by the Bauschinger effect. To obtain higher joint efficiency and fracture on the P-Al side, the joint should be made without higher forge pressure, and with the friction time at which the friction torque reaches the initial peak.

No abstract

This paper describes the effect of friction welding conditions on joining phenomena during the friction stage of type 7075-T6 aluminium alloy (A7075) friction welds. The friction torque had wear and seizure stages until the initial peak torque when A7075 was welded under high friction speed and low friction pressure, i.e. 27?5 rev s 21 and 30 MPa. Initial seizure and joining began at the central region (centre axis) of the welded interface, and extended towards the peripheral region (outer surface). On the other hand, when A7075 was welded under high friction speed and high friction pressure, i.e. 27?5 rev s 21 and 90 MPa, almost no wear stage existed before the initial peak torque. Initial seizure and joining began at the peripheral region of the welded interface and extended towards the central region. Then, the friction torque reached an initial peak torque when the welded interface was joined completely and upsetting of both base metals started. As a conclusion, the joining mechanism of A7075 friction welding was similar to that of low carbon steel.

No abstract

This report describes the observation resu]t of joining phefiomena in the friction stage, and an improvement of the conventional friction welding method with similur materials.The materials used were carbon steels and a brake type (direct drive) friction welding rnachine was used forjoining. As the improving friction welding method, relative speed was instantaneously rendiered te zcro at the end of each friction time. Tlie wear of beth surfaees stafted at periphery poftion (outer surface) of the joint and moved to center portion (center axis), Seizure and joining began at center portion and then extended toward periphery portion. The I'rietien torque rcached to initial peak torquc when the we]ded lnterface was joined completely and upsetting oi' both substrates started. It was determined that frictien we]ded joints with 100% joipt efficiency and good bend ductility cou]d be ebtained by using only the friction stage up to {nitial peak terque and without the need for the rbrging (upsetting) stage. As a conclusion, friction we]ded .ioints mude without using the forging stage has the same mechanica] propertles as those welded by the eonventional friction welding process including that stage,The friction we]ding methud without forging stage has [hc advantages of less burn-oft' (axia} shortening) and ]ess burr.1(by wortts .' friction veetding Relative spee4