Book consists of total of six chapters including theoretical backgrounds of electron beam welding and its spatiality from other welding processes specially to do different steel to Al-alloy welding. Our chosen material combinations are Fe 7%Al alloy to mild steel and DP600 steel to 5754-Al alloy and has been characterized comprehensively for defects and mechanical properties. Operating parameters studied included weld speed, with and without beam oscillation, and varying beam oscillation diameters. The joints were thoroughly inspected for their soundness using sub-micron X-ray radiography as well as 3D X-ray computed tomography. Major defects identified were porosity and Fe-Al intermetallics and their shape and size distribution are extensively quantified. Intermetallics are further characterized using lab source XRD, synchrotron diffraction, SEM, TEM. The solidification bulk texture is studied using neutron diffraction. Extensive microstructural investigation using SEM and TEM reveals heat mixing during beam oscillation. Evaluation of mechanical properties like microhardness, tensile, Charpy impact, Erichsen cup formability test is done following ASTM standards.