Explain briefly the four main microstructural mechanisms by which metals are hardened. Identify which mechanisms account for the following increases in yield stress (Note, there may be more than one):
(i) Pure annealed Al: 25 MPa; cold rolled non-heat-treatable Al-Mn-Mg alloy: 200 MPa
(ii) Pure annealed Cu: 20 MPa, cast 60-40 Brass (60% Cu, 40% Zn): 105 MPa
(iii) Pure annealed Fe: 140 MPa; quenched & tempered medium carbon steel: 600 MPa.
(iv) Pure annealed copper. 20MPa; nanocrystalline pure Cu: 500 MPa