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Stud joints of 5083 aluminum alloy were welded by arc stud welding and friction welding, and their joint strengths were examined. In the weld zone of the arc stud welded joint, no change occurred in the hardness distribution. In contrast, the weld zone of the friction-welded stud joint softened slightly on the plate side and hardened on the bar side. The tensile strengths of the arc stud welded joints with weld reinforcement and without weld reinforcement, and the friction-welded stud joints without burrs were 233, 231 and 180 MPa, respectively, and all joints fractured at the weld zone. In the bending test, all joints fractured near the weld zone at a bending angle of approximately 20°. In the fatigue test, the fatigue strengths of the arc stud welded joints were higher than those of the friction-welded stud joints, and the fatigue limits of the arc stud welded joints with weld reinforcement and without weld reinforcement, and the friction-welded stud joints without burrs were 43, 40 and 13 MPa, respectively.

Stud joints of 2017 aluminium alloy were friction welded and its joint strength was examined. A stair zone was formed at the weld interface. Although the hardness of the stair zone was almost the same as base metals, the heat-affected zone of the bar and the plate was softened. The tensile strength of joints tended to increase with a pressure and a friction time, and the highest tensile strength was 275 MPa (63.1% joint efficiency for the bar base metal). In the bending testing, joints were cracked in the weld zone at a bending angle of less than 5°. In the fatigue testing, joints fractured near the weld interface and the fatigue strength of joints increased as the tensile strength of joints was high.

Friction welding of SUS304 stainless steel to C1100 tough pitch copper was carried out and tensile strength of joints was examined. Also, a statistical analysis of the tensile strength data was investigated for judging a suitability of friction welding conditions on this joint. It was found that the SUS304 and the C1100 near the weld interface hardened and softened, respectively. There were fine-grained structures composed of much copper and a little of iron, chromium and nickel near the axial center at the weld interface. Tensile strength tended to increase with a friction time and with an upset pressure, and the maximum joint efficiency for the C1100 base metal was 101%. The shape parameter in Weibull distribution increased with an increase in mean value of tensile strength and with a decrease in dispersion of tensile strength. It seemed that the shape parameter is useful for judging the suitability of friction welding conditions.

t. Friction welding of FC250 common grade cast iron was carried out to examine the weldability and temperature distribution near the weld interface during welding. The joint strength of both solid and pipe joints was evaluated by tensile tests. The highest tensile strengths in the solid joints and pipe joints were 317 MPa (79% joint efficiency) and 381 MPa (95% joint efficiency), respectively. A fine-grained interfacial layer of FC250 formed near the axial center at the weld interface in the solid joints, whereas there was no fine-grained interfacial layer in the pipe joints. The welding material temperature at the axial center was higher than that at the periphery in the solid joint. There was little difference in the temperature distribution between the solid joints and pipe joints.

The relationship between joint strength and deformation heat input at the upset stage and the relationship between joint strength and upset bum-off length were examined on friction welded joints of 1050 pure aluminum to C1100 tough pitch copper. Joint quality was evaluated from the tensile strength and fatigue strength. It was found that both the deformation heat input at the upset stage and the upset burn-off length correlated well with joint strength. Additionally, when the deformation heat input at the upset stage or upset burn-off length exceeded a certain value, stable tensile strength was obtained. The mixing layer, intermetallic compounds of Al-Cu were interpolated into A1050, formed at the weld interface, and joints having a thick mixing layer fractured at the weld interface. Joint efficiencies of sound joints for the fatigue limit of the A1050 base metal were 88-100%. Judging from the fatigue limit, sound joints could be produced when either the deformation heat input at the upset stage or the upset burn-off length exceeded a certain value.

Conferring lightweight and good corrosion resistance, aluminium alloy joints are extensively required in the manufacture of various types of electrical and mechanical components. Research data previously obtained by the authors1, 2 show the efficiency of friction-welded joints, regardless of whether produced from similar or dissimilar materials, to be fairly well scattered under identical sets of friction welding conditions and underline the need for statistical analysis of a large number of joints to determine the suitability of any specific set of friction welding conditions. That is to say, joints with a high mean joint efficiency that are friction-welded under optimum friction welding conditions conform to a normal distribution with low scatter during such statistical analysis while simultaneously showing a large Weibull distribution shape parameter and small dispersion. On the other hand, joints with a low mean joint efficiency that are friction-welded under unsuitable friction welding condi...

Aluminum alloys to S25C carbon steel were friction welded, and the friction weldability and intermetallic formations at the weld interface of joints were investigated. Joints of A1050, A5052, A6061 and A6063 to S25C showed good-weldability, and A5056/S25C joint was somewhat poor than former one. An intermetallic compound of Al13Fe4 was formed at the weld interface of A5056/S25C and A6061/S25C joints, and their intermetallic formations were tend to increase with friction pressure, friction time and rotation speed. The joint strength of these joints was high when thin instermetallic conpound layer was formed under high upset pressure. Somewhat poor-weldability of A5056/S25C joint compared with A6061/S25C joint seemed a cause of the intermetallic formation accelated by high content of magnesium in A5056. Joints of A2011, A2017, A2024 and A7075 to S25C showed poor-weldability. Brittle intermetallic compounds of CuAl2 and Al7Cu2Fe were formed at the weld interface of A2011/S25C joint containing a copper.

Friction welding of S15CK carbon steel was carried out in order to examine the relationship between heat input for welding and joint strength. The joint strength is evaluated from tensile strength. The heat input is a heat source for welding solid materials and was classified into 6 inputs: friction heat input, deformation heat input and total heat input in the friction stage and upset stage.The most important heat input for evaluating the joint strength among these heat inputs was experimentally investigated through the tensile strength of joints welded under various welding conditions.As a result, it was made clear that the deformation heat input in the upset stage is much strongly related with the joint strength, and sound weld joints can be obtained deformation heat inputs more than about 100J/s. Moreover, it was recognized that the joint strength is possible to evaluate by the upset loss, therefore, sound welded joints can be obtained with about 1.2 mm upset burn-off length or more also.

Carbon steel was friction welded and torsion fatigue tests were conducted on weld joints having an upset burr in order to reveal the effect of an upset burr on fatigue strength. It was found that the fatigue strength of joints having a constant toe radius decreased with a decrease in hardness ratio (hardness of toe/hardness of base material). Softened joints (hardness ratio≤1) and hardened joints (hardness ratio>1) fractured at the toe of the upset burr and in the base material, respectively. On the other hand, the fatigue strength of joints having constant hardness ratio increased with toe radius. Using correlation analysis, a reasonable multiple regression equation was obtained between torsional fatigue strength and the fatigue factors, that is, the hardness ratio and toe radius of the upset burr. Thus, using this regression equation, the torsional fatigue strength of friction welded joints having an upset burr could be estimated.

Friction welding of 6061 aluminum alloy similar material was carried out in order to examine a relationship between heat input and joint performance. The joint performance is evaluated by tensile test. The heat input is a heat source for welding solid materials and is classified into six inputs, that is, friction heat input and deformation heat input during friction stage, upset stage and total stage respectively. The most important heat input for evaluating the joint performance among these heat inputs was experimentally investigated through the tensile strength of joints welded with many welding conditions because the friction welding mechanism is so complexed. As the results, the deformation heat input during upset stage was much related with the joint performance, and sound welded joints were obtained with 200 J/s or more deformation heat input. Moreover, it was recognized that the deformation heat input during upset stage was in proportion to the upset loss, therefore, sound welded joints were obtained with 3 mm or over upset loss also.

Friction welding of various aluminum alloy pipes to SUS304 stainless steel pipe was carried out making clear weldability at dissimilar material pipe. A1050/SUS304, A5052/SUS304, A5056/SUS304, A6061/SUS304 and A6063/SUS304 joints showed good weldability and the maximum joint efficiencies of these joints in tensile test were about 91%, 71%, 60%, 79% and 97%, respectively. In these cases, the formation of Al13Fe4 intermetallic compound was induced by the interdiffusion through the weld interface. On the other hand, other joints had poor weldability. In the cases of A2011/SUS304, A2017/SUS304 and A2024/SUS304 joints, CuAl2 and Al7Cu2Fe were observed on the friction surface, and the maximum joint efficiencies of these joints were about 26%, 39% and 32%, respectively. For the case of A7075/SUS304 joint, Al23CuFe4 was observed on the friction surface, and the maximum joint efficiency was about 37%.

Friction welding of 2017 and 6061 aluminum alloys in as-received, solution heat treated and aged states was conducted under the optimum welding condition for as-received specimens. As friction-welded, tensile strength ofjoints was approximately equal to the mother 6061 alloy for every temper states. When the joints were post-heat-treated, brittle fracture occurred at the welding interface and/or pan-cake-like recrystallized boundaries in the vicinity of the interface. A mechanism of friction welding and an origin of embrittlement were discussed on the basis of the effects of heat treatments, on the hardness distribution changes of the joints and also on the fractographical features of tensile specimens.

Destructive test of the joints was carried out for examining the impact and fatigue strength. The softened area of A6061 side of the joints welded under a higher upset pressure is narrower compared with that welded under a lower upset pressure, because the softened area of A6061 side was expelled as the upset burr by the action of upset pressure. The dynamic strength of the joints depends on the width of the softened area of A6061 side. In the case of smoothed impact specimen, the impact absorbed energy of the joints increases with increase in upset pressure, while it decreases with the upset pressure over 240 MPa. On the other hand, no smoothed specimens of A6061 base material fracture. In the case of notched specimen, the impact absorbed energy of the joints welded under the upset pressures over 160 MPa remains to be almost equal to the maximum value, and the maximum joint efficiency is about 15%. The impact fracture occurres both in the mixed area of the weld interface and in the softened A6061 area. The fatigue strength at a given endurance (number of cycles to failure 107) of A6061 base material and the joints welded under 120 MPa and 240 MPa upset pressure are 121 MPa, 112 MPa and 122 MPa, respectively. The fatigue fracture of the joints occurres in the softened A6061 area or in the mixed area of the weld interface and the softened A6061 area depending on the welding conditions.

The optimum welding condition for brake type friction welding of titanium and SUS304 stainless steel was investigated using a response surface method. The optimum friction pressure, forging pressure, friction time and rotating speed of welding were determined as 91MPa, 195MPa, 0.8s and 1842rpm, respectively. The joint welded in CO2 gas had higher tensile strength than that welded in air. The transformation of α-Ti into β-Ti and γ-Fe(Cr) into α-Fe(Cr), and the formation of intermetallic compound (Fe(Ni)•Ti) were induced by the interdiffusion along the welding interface. The joint strength depends on the width of β-Ti and Fe(Ni)•Ti layer.