Digital Repository, CONVEGNO IGF XXII ROMA 2013

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Fracture behaviour of grain refined A356 cast aluminium alloy: tensile and Charpy impact specimens
D. Casari, A. Fortini, M. Merlin

Last modified: 2013-06-27


The excellent combination of high strength/weight ratio, high impact toughness, very good
castability, low thermal expansion coefficient and corrosion resistance make Al-Si cast alloys suitable for the
production of components like rims, engine and gear parts. Even though it is well-known that mechanical
properties are closely related to secondary dendrite arm spacing (SDAS), the influence of grain size has to be
considered as well. A fine and equiaxial grain structure is generally obtained through specific products, called
grain refiners, which are added to the melt alloy in form of cans, bars, tabs, waffles, ingots and granulated
fluxes. In this study three commercial Ti-B based grain refiners were added to the A356 (Al-Si-Mg) aluminium
alloy. A number of 20 castings was obtained through permanent mould casting, n°5 for each experimental
condition, named Reference (not refined), GR1, GR2 and GR3. Tensile and Charpy impact specimens were
drawn by means of machining, T6 heat-treated and then tested. The influence of the grain refiners was assessed
according to the experimental data of tensile and impact tests. Experimental results were compared to OM and
SEM fracture observations, pointing out the effect of the different grain refiners on fracture mechanism.
Although both impact and tensile specimens showed a mixed transgranular-intergranular fracture mode, it was
found that impact samples were deeply influenced by the refiner added, while this effect was less pronounced
for the tensile ones. Fractographic observations also revealed the role of Fe based intermetallic compounds in
terms of fracture behaviour.

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