Engineering

MIE 302 -- Mechanical Engineering Laboratory I

Experiment 3

Property Modification of Alloys

(1 week) (revised 7/05)

Objectives: To demonstrate quantitatively the role of cold work and annealing on the strength, ductility and hardness of 70/30 brass.

Equipment: Rockwell hardness tester, Instron tester and extensometer

Rolling mill

High temperature furnace

Material: Alloy 260 Cartridge Brass (approx. 70 w% copper and 30 w% zinc) - annealed at 560oC for one hour.

Pre-Lab: Discuss the principle of cold work. Define percentage cold work. Provide background information on how hardness, strength and ductility change with %cold work. Must show graphs to illustrate the trends. Discuss why the indicated changes occur.

Discuss the principle of annealing and its effect on hardness, strength and ductility. Show illustrative graphs and discuss the three stages of annealing and the meaning of recrystallization temperature.

3. Procedure: Each laboratory group will be given two tensile specimens of annealed brass. The tensile properties of the control specimen in the as-received condition (no cold working) is provided to you. The two specimens will be cold-worked to a fixed percentage cold work. Following cold working hardness measurements are taken on each sample and then one of the samples is subjected to a tensile test in the Instron machine to obtain the full stress versus strain curve. The second sample is then annealed at a fixed temperature. Following annealing the hardness of the sample will need to be measured. Make sure that hardness measurement is made only after the specimen has completely cooled to room temperature. Next, the sample will need to be tested in the instron machine to determine tensile properties. The actual cold work amounts and annealing temperatures will be as per instructions of the lab instructor.

Safety Procedures: When loading and unloading a high temperature...