Friction stir welding is a solid state joining technique in which no melting of the metals is involved. The technique is very attractive for aluminum alloys due to the low heat input involved in the process, which leads to improved mechanical properties as compared to conventional fusion welds. In this work, different aluminum series alloys were friction stir welded together. The aluminum alloys consisted of a solid solution/strain hardened aluminum alloy 5083-H131, and precipitation strengthened aluminum alloys 2139-T8 and aluminum 7085-T721. The joint combinations were aluminum alloys 5083-H131 to 7085-T721, aluminum alloys 2139-T8 to 7085-T721, and aluminum alloys 5083-H131 to 2139-T8. Their mechanical properties were analyzed and compared to base metal properties. Optical microscopy was used to analyze the grains in the welds. Good mixing of the different aluminum alloys was optically observed in all of the welds, which lead to good joint properties, opening the possibilities to build structures with superior performance.