Dissimilar material pipe joints are used frequently as a conduit which passes gas liquid, and also for the purpose of a reduction in product weight and material cost. In the production of such joints, friction welding is most effective processbecause it is possible to make the thin compound layer at the weld interface by the operation of high axial pressure. However the process has the characteristic that the formation of burr is indispensable. In the case of pipe joints, the inside and theoutside burrs are formed, especially the inside burr obstructs the flow of a fluid.In this study, 606l aluminum alloy pipe and S45C carbon steel pipe were friction welded and the effects of thickness ratio on joint strength and burr shape were investigated. The main results obtained are as follows.As to the tensile strength of pipe joints composed of various thickness ratio welded under the constant welding condition, the joint strength of pipe of large thickness ratio was low so that increasing the thickness ratio of weld pipe required more largeforging pressure in order to obtain the same as the joint strength and the burn- off quantity of pipe of small thickness ratio. The average joint efficiency of weld joints seemed to be excellent was 57.3%. The burr progressed complicatedly as the weldingtime elapsed, that is, the outer burr spread to the radial direction along the aluminum alloy following by curl back of the tip of burr, on the other hand, the inner burr grew to the thrust direction along the carbon steel rather than spreading to theradial direction. An experimental equation which estimates the hollow diameter d{sub}i from the outside burr diameter d{sub}0 was introduced as follows.d{sub}i= 0.058d{sub}0{sup}2 -2.998d{sub}0+47.656.Also, the estimation of hollow diameter was more easy using the neural network which was composed of 3 input units of outer diameter of pipe, outer burr height and burn-off quantity or 4 input units of outer diameter of pipe, outside burr height, burn-off quantity and width of outer burr
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