Indriyati, Martha (2016) Effect of TiB2 addition on the microstructure and mechanical properties of Al-Cu-Mg-Ag alloy. PhD thesis, University of Warwick.

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Abstract

The influence of addition of 0.2 wt.% Ti + 4.5 wt.% TiB2 particles on the workability and static softening behaviour of Al-Cu-Mg-Ag matrix alloy has been compared with matrix alloy, Al-Cu-Mg-Ag, and Al-Cu-Mg-Ag alloy containing 0.2 wt.% Ti. In this study, the workability has been explored through compression test, rolling and extrusion. Furthermore, a mechanical property in tension, both in room temperature and elevated temperature was also carried out. Detailed characterisation on the distribution of TiB2 particles as well as Al3Ti particles in each of material processing stages i.e. casting, homogenisation, rolling and extrusion are presented.

The flow stress behaviour obtained from compression testing showed a similar trend for all three materials in which the flow stress increases with decreasing temperature and increasing strain rates. In all test conditions, 0.2Ti-4.5TiB2 composites exhibited the highest flow stress of all materials. Interesting finding was obtained in which with increasing temperature and decreasing strain rates, 0.2Ti-4.5TiB2 composites exhibited closer flow stress with other two alloys. Owing to the existence of TiB2 clusters around grain boundaries and triple joints as well as blocky Al3Ti particles in the as-cast conditions which will increase strain hardening during deformation, this finding was not expected. This result indicates that at higher temperatures and low strain rates, the addition of TiB2 particles would not give a significant influence to the deformation mechanism. Dynamic recovery was observed in all test conditions of matrix alloy and 0.2Ti alloy. In contrast to that, in 0.2Ti-4.5TiB2 composites, dynamic recrystallisation was observed upon low temperature and high strain rate deformation, while dynamic recovery with localised dynamic recrystallisation was observed upon high temperature and low strain rate deformation.

Another interesting finding was achieved regarding static softening behaviour of 0.2Ti-4.5TiB2 composites. Recrystallisation was retarded in 0.2Ti-4.5TiB2 composites. Large and elongated recrystallised grains were observed following annealing of the rolled product of 0.2Ti-4.5TiB2 composites. Furthermore, fine recrystallised grains were observed in the vicinity of Al3Ti particles and TiB2 clusters. This result was also unexpected since owing to the high volume fraction of secondary particles in the composites, one would expect high recrystallisation rates due to potential nucleation in the vicinity of secondary particles. This behaviour was explained in terms of the distribution of TiB2 particles. TiB2 particles were found pinning the grain boundaries during annealing, inhibiting grain boundary migration and hence leading to the retardation of recrystallisation. Consequently, a large recrystallised grain size was observed in the 0.2Ti-4.5TiB2 composites. On the contrary, more equiaxed recrystallised grains were observed in the matrix and 0.2Ti alloy. In addition to that, a deformed structure was retained following annealing of extruded 0.2Ti-4.5TiB2 composites, suggesting retardation of recrystallisation.

Regarding the mechanical properties, higher tensile strength was observed in 0.2Ti-4.5TiB2 composites, both at room temperature as well as at a temperature of 200°C. Furthermore, concerning the superplastic behaviour of the composite, a limited processing window was observed in which the highest elongation of 151% was obtained at the temperature of 475°C. Elongation was decreased with further increasing temperature. This was postulated as being due to liquation at higher temperature.

Item Type:	Thesis (PhD)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Library of Congress Subject Headings (LCSH):	Aluminum alloys -- Mechanical properties, Aluminum alloys -- Microstructure, Titanium diboride -- Industrial applications, Aluminum alloys -- Compression testing, Superplastic forming (Metal-work)
Official Date:	October 2016
Dates:	Date Event October 2016 Submitted
Institution:	University of Warwick
Theses Department:	Warwick Manufacturing Group
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Dashwood, Richard J. ; Janik, Vit
Sponsors:	Aeromet International Ltd.
Format of File:	pdf
Extent:	xxiii, 195 leaves : illustrations, charts
Language:	eng

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