Grain Refinement and its Effect on Mechanical Properties

Leung, Jeffrey (2013). Grain Refinement and its Effect on Mechanical Properties Honours Thesis, School of Engineering, The University of Queensland.

       
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Author Leung, Jeffrey
Thesis Title Grain Refinement and its Effect on Mechanical Properties
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2013
Thesis type Honours Thesis
Supervisor Mingxing Zhang
Total pages 82
Language eng
Subjects 0913 Mechanical Engineering
Formatted abstract
Pure Zinc contains good strength, but is rarely used for casting due to its low strength and cannot be used for high temperature applications. It also contains low creep strength, ductility and hardness. Therefore, it is common for Zinc to pair with another alloying element such as Aluminium, Copper and Magnesium. Moreover, Zinc alloy is used for galvanic protection and also used in die casting. Its advantages include fast rate of die casting due to its low melting point, corrosion resistant, and ability to form a coating on steel. Zinc cannot be strainhardened significantly as it recrystallises and creeps near room temperature. Moreover, it contains sufficient strength for most applications and the cost of Zn is similar to Al and Cu alloys. Its disadvantages include loss of strength and hardness at temperature higher than 95oC due to creep at room temperature. Moreover, it contains relatively high density in comparison to Al which decreases its suitability in places where weight is important. Its HCP structure also limits the plastic deformation properties.

Currently, there lacks sufficient research on the grain refinement of Zinc in regards to mechanisms and its effect on the alloy’s mechanical properties. Zinc alloy have been developed to improve corrosion protection, control the coefficient of friction, temperature and wear resistance. Another form of Zn alloy is Zn-Ni which prevents hydrogen from penetrating into steel substrate and causing problems associated with hydrogen embrittlement. This is useful for hard strength and tool steels susceptible to hydrogen embrittlement.

Zinc is brittle but its strength and ductility can be improved through grain refinement. This occurs by reducing the grain size and increasing the number of grains via solute theory and heterogeneous nucleation. As the grain size is reduced, the space between grains is also reduced which increases the number of grain boundaries. Grain boundaries are major hurdles for dislocation movement which causes failure through yielding and reduces the alloy’s ductility. It is theorised that grain refinement will rectify this problem.
Keyword Grain Refinement

Document type: Thesis
Collection: UQ Theses (non-RHD) - UQ staff and students only
 
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Created: Thu, 03 Dec 2015, 15:16:32 EST by Asma Asrar Qureshi on behalf of Scholarly Communication and Digitisation Service