A. explain briefly the four main microstructural mechanisms by which metals are hardened. identify which mechanisms account for the following increases in yield stress (nb there may be more than one): i. pure annealed aluminum: 25 mpa; cold rolled non‐heat‐treatable al‐mn‐ mg alloy: 200 mpa ii. pure annealed copper: 20 mpa; cast 60‐40 brass (60% cu, 40% zn): 105 mpa iii. pure annealed iron: 140 mpa; quenched & tempered medium carbon steel: 600 mpa. iv. pure annealed copper: 20mpa; nanocrystalline pure cu: 500 mpa. b. for each of mechanisms (i) – (iii) in part (a), give other examples of important engineering alloys which exploit these mechanisms.