This work developed a friction-stir-welding system for thin wall pipes and realized high performance Al/Cu pipe joining.Five kinds of intermetallic compounds(IMCs) with different characteristics has been found through macro-/micro-scale observation.The contents of IMCs have been detected to be Al
2
Cu
Al
4
Cu
9
and AlCu(small amount) through X ray diffraction and nanoindentation.Different shear effect and pressure effect by welding tool were found to be the main formation mechanisms of different kinds of IMCs through further research and analysis.