The Effect of Ultrasonic Melt Treatment on Macro-Segregation and Peritectic Transformation in an Al-19Si-4Fe Alloy
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AL-SI based alloys are the most widely used Al-based foundry alloys due to their excellent combination of mechanical properties and ease of castability. Hypoeutectic Al-Si alloys containing 5 to 12 wt pct Si (wt pct is used hereinafter unless otherwise specified) account for most commercial production. However, hypereutectic Al-Si alloys with 14 to 25 pct Si are more desirable for applications requiring wear resistance, along with high strength and low weight. Transition metal solutes, notably Fe, Cr, and Ni, in these alloys can further improve their performance at elevated temperatures due to the presence of thermally stable intermetallics.[1,2] The use of Fe is considered to be C.J. TODARO, M.A. EASTON, M. QIAN, and D. QIU are with the Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne, VIC 3000, Australia. Contact e-mail: [email protected] D.H. StJOHN and G. WANG are with the Centre for Advanced Materials Processing and Manufacturing (AMPAM), School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, QLD 4072, Australia. Manuscript submitted April 17, 2017. Article published online September 18, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
particularly attractive for two reasons: it alleviates die soldering for die casting and allows the use of secondary Al (post-consumer scrap) already containing appreciable amounts of Fe. However, the amount of Fe addition is restricted as the resulting Fe-containing intermetallics can form as large and coarse platelet-like features, deteriorating ductility and fracture toughness.[3] Moreover, it is challenging to obtain microstructurally homogeneous castings of hypereutectic Al-Si-based alloys by conventional foundry processes, because of the propensity to form macro-segregation defects during solidification.[4] As a result, special solidification processes such as rapid solidification,[5] spray deposition,[6] melt thermal-rate treatment (MTRT),[7] and ultrasonic melt treatment (USMT)[8–13] have been employed to control the size, morphology, and distribution of Fe-containing intermetallics and primary Si in hypereutectic Al-Si alloys. In Fe-containing hypereutectic Al-Si alloys, the Al-Fe-Si phase diagram[14] shows that the following three reactions can occur leading to the formation of b-Al5FeSi during equilibrium solidification: (1) (2)
L + d-Al3FeSi2 fi b-Al5FeSi + Si L fi b-Al5FeSi + Si VOLUME 48A, NOVEMBER 2017—5579
11 12 8 10 9
13
to 20 to 20
no no no no no Mn = 0.8 Si Mn = 0.4, 0.8 Si none d-phase Co = 0 to 1.5 Si Mn = 0.0, 0.5 Si 2 2 4 0.7 2 17, 17, 18, 20, 20,
5580—VOLUME 48A, NOVEMBER 2017
Note: The difference in pouring temperature refers to the difference in pouring temperature used without and with USMT. NS.: not specified.
1600 1600 1200 1200 1200
NS NS 20 NS NS
20 20 19 20 20
NS NS NS NS NS
15 15 10 15 15
to 20 to 20
1300no difference 600 85 to 125 600 110 240 Not poured 600 135 600 130 room temp. N/A 19.5 25 to 30 2000
phases not stainless steel cruciblecharacterized type no effect T
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