I know this is a long question but please show full detailed

Question No.2 C6) (a)A I kg Pb-Mg alloy with a Mg concentration of 50 wt% is slow cooled from 700 C to 450 C. i) sketch, using proper labeling techniques, the microstructures at 600 C, 500 C. and 450 C. (6 marks) 1) The weight percentage of a and Mg2Pb 2) The weight percentage of the eutectic material 3) The distribution of Mg amongst the various grains in grams. iii) Identify and name the invariant points on the Pb-Mg phase diagram. Be sure to provide the relevant transformation equations, temperature and composition. (4 marks) (4) (b) Name and describe two forms of corrosion. For each form, suggest a method of prevention. 200 Composition Pti

Solution

This is one of the SOLDER metal diagrams. microstructures are very similar

1. Microsrtructure at 600 ( liquid phase if quenched will show uniform field no ppts

at 500 portions of alpha phase will appear

at 450 will get alpha and Mg2Pb

2 wt % of alpha and Mg2Pb at Co 50% of Mg

Use lever rule: tie line at 450 intersects the phase lines at 36 alpha and 80 Mg2Pb

wt% Mg2Pb (50-36)/(80-36) =14/44

wt% alpha = 80-50/44 = 30/44

ii) wt % of eutectic material: eutectic point at 67%. Draw tie line centred at O the nominal conc of 50% and take one end to eutectic comp 67% and other to alpha line of about 36 %.

Wt % by lever rule is (50-36)/(67-36) =14/30

iii) distbn of Mg among the various grains in gms. The % of Mg will follow the solvus line on the LHS of the diagram, as temp is reduced, the proportion of Mg reduces, meaning it is precipitated out as part of the Mg2Pb phase

B) The invariant points on the diagram are the eutectic points

One is at 66% Pb, 520 C and the other at about 95% Pb 260C

Corrosion: due to oxidation, due to embritttement.   Alloying may help, surface coatings are another means