13. a) How can you explain the term of age hardening process? Please explain stages and give detailed information by giving an example. b) What is the difference between precipitation and dispersion strengthened alloys? 14. Explain why, under some circumstances, it is not advisable to weld a structure that is fabricated with a 3003- aluminum alloy. Hint: strengthening of a 3003 alloy is accomplished by cold working. 800 A Eutectoid temperature 1400 15. Using the isothermal transformation curve shown to the right for the Fe-C system, determine the final structure of the Fe-C alloy for the following cooling processes (assume all processes start as homogeneous austenite above 760 C): a) Rapidly cool to 600 C, hold for 102 second, rapidly cool to room temperature; 700 A 600 500 Temperature (C) 400 T T 1200 1000 800 A 600 b) Rapidly cool to 350C, hold for 10 seconds, rapidly cool to room temperature; 300 Mistart) 50% 200 M+A 400 M(50%) M(90%) 100 200 c) Rapidly cool to 300 C, hold for 10 seconds, rapidly cool to room temperature. 10-1 1 10 102 Time(s) 103 104 105 Temperature (F)