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Metal 259 - Fall-1995 - Exam 1

Par time - 7 min. (Time required to read questions, think a little, and write answers)

1. Put your social security no. on the line above now.

2. For the questions below, only short answers are required.....usually only a few words. Thus, only a small amount of space in each has been left for your answer; only answers placed in the space provided will be considered. Diagrams and drawings, where appropriate, are welcome. Many hours will be required to grade this exam; you can help us (read as "get your graded exam back sooner") by writing clearly and as succinctly as possible.

3. (10) List three ways in which the tensile strength of steels can be increased.

a. add carbon

b. add alloying elements

c. quench & temper......................another answer: cold work

4. (10) Explain the AISI/SAE steel designation code.

xxyy

xx tells about the alloy element content - arbitrary numbering system.

yy is the carbon content as 0.yy w/o

5. (10) What is the basis for the Aluminum Association classification system (discussed in class) for wrought aluminum alloys?

principal alloying element determines z in zxxx number for Al alloy

6. (10) Suppose we have an Al-4%Cu alloy. Slow cooling and rapid cooling (quenching) of this alloy produce materials with different structures and properties.

a. What fundamental atomic process is prevented from taking place in rapid cooling?

diffusion

b. Rapid cooling produces a structure with ____one_______ phase(s) and slow cooling

produces a structure with ______two_____ phase(s). 

7. (10) Why are solid solution alloys harder than the corresponding non-alloyed pure metal?

distorted slip planes due to different atomic sizes. dislocs have more difficulty mmoving over these distorted slip planes

8. (10) A brass alloy is to be used in an annealed condition. Since the alloy will not be work hardened and cannot be precipitation hardened, what can be done to the grain structure to strengthen the material?

decrease grain size

9. (10) Compare the ductilities of metallic, ceramic, and polymeric materials.

metallic - moderate

ceramic - zero

polymers - thermoplastic very large, thermosetting zero

10. (10) Show below how the fracture energy upon impact varies with test temperature. Mark axes.

S-shaped curve with lower shelf energy at low temps. and higher shelf energy at high temps., with gradual transition between them

11. (20) Define:

a. Yield strength

stress req'd to produce plastic deformation...read from test curve at 0.2% offset

b. Hardness

resistance to indentation

c. Dislocation

line defect responsible for plastic deformation

d. Slip plane

plane in crystal along which disloc moves

e. Phase

mat'l or portion of material which is homogeneous in composition and has a specific atomic arrangement (crystal structure)