Damping properties of A357 alloys and A357-stainless steel composites fabricated under different conditions
The lab scale gravity casting technique was used to produce alloy specimens of nonsuperheated A357 alloy, superheated A357 alloy and composite specimens of superheated A357-0.5 and 1.0 wt.% stainless steel composites. The primary cast ingot A357 alloy was melted in graphite crucible before pourin...
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| Format: | Thesis |
| Language: | English |
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| Online Access: | http://dspace.unimap.edu.my:80/xmlui/bitstream/123456789/20553/2/Full%20Text.pdf http://dspace.unimap.edu.my:80/xmlui/bitstream/123456789/20553/4/Page%201-24.pdf |
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| Summary: | The lab scale gravity casting technique was used to produce alloy specimens of
nonsuperheated A357 alloy, superheated A357 alloy and composite specimens of
superheated A357-0.5 and 1.0 wt.% stainless steel composites. The primary cast ingot
A357 alloy was melted in graphite crucible before pouring into the stainless steel
mould at 700ºC for all specimens. Meanwhile, prior to pouring, the preform of 304
stainless steel wires were aligned in stainless steel mould to produce superheated
A357-0.5 and 1.0 wt.% stainless steel composites respectively. The main objective of
this research is to study the effect of superheating on the microstructures and dynamic
mechanical properties, to identify the phases that presents in all the specimens and
also to identify the appropriate damping mechanisms in all specimens at lower and
elevated temperatures. The superheating had refined the eutectic Si particles and
changed the shapes of α-Al dendrites in superheated A357 alloys. The superheating
also changed the shapes of π-Al8FeMg3Si6 intermetallic phase and Mg2Si phase in
superheated A357 alloys. Superheated A357-0.5 wt.% stainless steel composite
showed poor bonding and less intensified of coarser eutectic Si particles around the
matrix-reinforcement interface. Superheated A357-1.0 wt.% stainless steel composite
showed good bonding and more intensified of finer eutectic Si particles around the
matrix-reinforcement interface. However, no interface reaction layer was observed at
the matrix-reinforcement interface of the composite specimens. Dynamic mechanical
properties such as storage modulus, loss modulus and damping capacity were
investigated by dynamic mechanical analyzer (DMA). Superheated A357-1.0 wt.%
stainless steel composite showed the highest storage modulus of 66.30 GPa at 50ºC.
Superheated A357-0.5 wt.% stainless steel composite showed the highest loss modulus
of 4.10 GPa at 380ºC. Superheated A357 alloys showed the highest damping capacity
of 0.0842 GPa at 380ºC. Dislocation damping was the mechanism at lower
temperatures range (50 to 280ºC) for the alloys and the composites. Meanwhile, grain
boundary damping and interfacial damping were the mechanisms at elevated
temperatures range (281 to 380ºC) for the composite and only grain boundary
damping was the mechanism at elevated temperature range for the alloys. Differential
scanning calorimetry (DSC) study at lower temperatures range (100 to 450ºC) of
solution treated alloys and composite specimens showed the presence of two
exothermic reactions (precipitation of θ″ and θ′) and an endothermic reaction
(dissolution of θ″) while at elevated temperatures range (530 to 630ºC) of solution
treated alloys and composite specimens showed three endothermic reactions (Al
dendrites, Al + Si and Al + Si + Mg2Si + π-Al8FeMg3Si6). |
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