This lecture discusses the hexagonal lattice structure in magnesium and titanium, focusing on the c/a ratio, slip systems, and dislocation motion. It also covers the deformation behavior of polycrystalline magnesium and its alloys at different temperatures, emphasizing the role of critical resolved sheer stress and diffusion-controlled mechanisms. Furthermore, it explores strengthening mechanisms in materials, such as grain boundary strengthening, solid solution strengthening, and precipitation hardening. The lecture delves into the concept of long-range order in intermetallic structural alloys, the lattice structure of NiAl, and the brittleness of these alloys at room temperature. It concludes with a failure case analysis of undercarriage trunnion failure and a broken wire cutter, highlighting fracture mechanisms, stress analysis, metallographic evaluations, and conclusions drawn from the investigations.