Focus: HOPE (FH) has developed the process parameters to successfully join AA6061 aluminum alloy and High Hardness Armor (HHA) steel using the friction stir process (FSP). Metallographic analysis conducted at the FH metallurgical laboratory, and later at the TARDEC metals lab, has confirmed that the dissimilar metals were metallurgically bonded at the joint surface with a thin (2-5 microns) Al-Fe intermetallic present. Mechanical load testing determined that the bimetallic FSP joint was stronger than similar AA6061-to-AA6061 fusion-welded and FSP joints. Initial process parameter trials were conducted to define the operating envelop for this FSP application. FH then evaluated the friction stir process parameters using an orthogonal array methodology. The parameters studied included tool rotation speed, tool traverse rate, tool tilt angle, plunge tool rotation speed, plunge rate, dwell, and joint offset. Other factors that were evaluated include tool design, fixture cooling, and auxiliary induction heating. In total 123 sets of process parameters were evaluated. Using the process parameter set which exhibited the greatest tensile strength FH produced a series of joint coupons which were then machined into test specimens for mechanical characterization. Metallographic samples were also prepared and analyzed using optical microscopy, scanning electron microscopy (SEM), electron back scatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS). This report also includes a description of the induction pre-heating system that was designed and demonstrated during this project for the potential use for FSP of high hardness metal alloys.