MAT4443


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Spring 2019-2020 Exam

METALLURGICAL PROCESSING

Expected Duration of Exam: 1 Hour, 30 Minutes

There are THREE Questions
Answer ALL Questions



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Department Of
Materials
Science &
Engineering.

MAT4443
2
MAT4443

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1. Various factors such as the quality of the starting material, and the correct choice
of process parameters including temperature and strain rate are vital in avoiding
defect formation and ensuring good productivity in metal forming operations.

(a) An aerospace extrusion company wishes to use an indirect extrusion press
with a maximum capacity of 9.5MN to extrude an aluminium alloy billet of
120mm diameter to a rod of 20mm diameter at a temperature of 450° C.
Showing your working, calculate whether the extrusion temperature has been
correctly chosen given that:

● the flow stress of the material at 450°C is 120 MPa
● the extrusion constants a and b are 0.8 and 1.8 respectively
● the container diameter is equal to the billet diameter

and suggest any improvements or changes to the process route if necessary.
[10 marks]

(b) What are the factors that could cause surface cracking during the extrusion of
aluminium? [2 marks]

(c) Explain why the quality of the starting material plays a crucial role in avoiding
defects during steel wire drawing. [2 marks]

(d) Why are billets extruded using indirect extrusion sometimes scalped before
processing? [2 marks]

(e) Calculate the optimum approach angle when a circular wire of 8mm is reduced
in one step to a diameter of 5mm. The friction coefficient in this case is taken
to be 0.2. [4 marks]



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MAT4443
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MAT4443
2. Continuous casting accounts for about 95% of the world’s cast steel and can be
thought of as a sequential process with each part of the process playing an
important role in the overall success of the final cast product.

(a) Why are some steels not suitable for continuous casting? [2 marks]

(b) What is the function of a Z band on a submerged entry nozzle? [1 mark]

(c) Describe, with specific reference to the avoidance of defects in the finished
product, the important features of the following with respect to the continuous
casting process.

i. the tundish
ii. the mould
iii. mould fluxes
[9 marks]

(d) Describe two methods by which the viscosity of mould fluxes might be
measured. [4 marks]

(e) Why is it important to be able to control the flow of the steel throughout the
casting process? Describe two methods by which this can be achieved.
[4 marks]


3. The vertical forming pressure for axisymmetric compression can described by:















D
r
h
D
Yp
2
1exp



(a) Explain the significance of the terms in the above expression. [3 marks]

(b) Describe under which conditions the value of p in the above expression will be
at a maximum and minimum. [5 marks]

(c) Assuming that axisymmetric compression is conducted on a solid disk (10 cm
diameter, 2.5 cm height), calculate the maximum pressure at the onset of
plastic flow, given that the yield stress is 345 MPa and the average coefficient
of friction is 0.10. [6 marks]

(d) Determine the expression for the horizontal forming pressure (q), and calculate
its minimum value. [6 marks]


END OF QUESTION PAPER

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