Variation of Properties in the Cross-Section of Semi-Solid Al-7Si-0.3Mg Castings


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In semi-solid casting, a slurry consisting of primary α-Al crystals and liquid is injected into the die cavity. The solidification in the die-cavity occurs by the growth of the primary α-Al crystals formed during slurry preparation and in the shot sleeve, nucleation and growth of in-cavity solidified crystals and ends with the eutectic reaction. During solidification in the die cavity, the cooling rate near the die wall is higher in comparison to the centre of the casting, particularly for thick-walled castings. The solidification conditions for the slurry α-Al crystals that are closer to the die wall can be very different compared to the slurry α-Al crystals located at the casting centre. This can result in different solute concentration in the interior of the α-Al globules in different regions of the semi-solid casting cross-section and consequently, different response to heat treatament. The RheoMetal™ process was used to produce thick-walled semi-solid castings. Semi-solid castings in the as-cast and T6 conditions were investigated. Indentation tests for hardness measurements in the nano-range were performed in the interior of α-Al globules near the surface and at the casting cross-section centre. The hardness variation across the casting cross-section was evaluated by low-force Vickers hardness. The castings in the as-cast condition showed more uniform properties in the cross-section compared to the T6 condition. Additionally, the results suggest that microsegregation in the interior of α-Al globules is very low in castings in the as-cast and T6 conditions.



Solid State Phenomena (Volume 285)

Edited by:

Qiang Zhu, Ahmed Rassili, Stephen P. Midson and Xiao Gang Hu




J. Santos et al., "Variation of Properties in the Cross-Section of Semi-Solid Al-7Si-0.3Mg Castings", Solid State Phenomena, Vol. 285, pp. 81-86, 2019

Online since:

January 2019




* - Corresponding Author

[1] M.C. Flemings, Behavior of metal alloys in the semisolid state, Metall. Trans. B. 22 (1991) 269–293..

[2] H. Atkinson, Semi-solid processing of metallic materials, Mater. Sci. Technol. 26:12 (2010) 1401–1413..

[3] M. Hitchcock, Y. Wang, Z. Fan, Secondary solidification behaviour of the Al-Si-Mg alloy prepared by the rheo-diecasting process, Acta Mater. 55 (2007) 1589–1598..


[4] S. Otarawanna, C.M. Gourlay, H.I. Laukli, A.K. Dahle, Formation of the surface layer in hypoeutectic Al-alloy high-pressure die castings, Mater. Chem. Phys. 130 (2011) 251–258..


[5] H. Möller, G. Govender, W.E. Stumpf, P.C. Pistorius, Comparison of heat treatment response of semisolid metal processed alloys A356 and F357, Int. J. Cast Met. Res. 23 (2010) 37–43..


[6] G. Govender, H. Möller, Evaluation of surface chemical segregation of semi-solid cast aluminium alloy A356, Solid State Phenom. 143 (2008) 433–438.


[7] A. Abou Antoun, M. Brochu, H. Möller, Effect of the rheocasting process and of the SLS layer on the fatigue behavior of 357 aluminum alloy, Solid State Phenom. 217–218 (2014) 227–234..


[8] S. Ji, H. Yang, X. Cui, Z. Fan, Macro-heterogeneities in microstructures, concentrations, defects and tensile properties of die cast Al–Mg–Si alloys, Mater. Sci. Technol. (United Kingdom). 33 (2017) 2223–2233..


[9] M. Blad, B. Johannesson, P. Nordberg, J. Winklhofer, M. Blad, B. Johannesson, P. Nordberg, Manufacturing and fatigue verification of two different components made by semi-solid processing of aluminium TX630 alloy, in: Semi-Solid Process. Alloy. Compos. XIV, Trans Tech Publications, 2016: p.328–333..


[10] O. Granath, M. Wessén, H. Cao, Determining effect of slurry process parameters on semisolid A356 alloy microstructures produced by RheoMetal process, Int. J. Cast Met. Res. 21 (2008) 349–356..


[11] SS-EN ISO 6507-1:2018, Metallic materials - Vickers hardness test - Part 1: Test method, (2018).

[12] M. Payandeh, A.E.W. Jarfors, M. Wessén, Solidification sequence and evolution of microstructure during rheocasting of four Al-Si-Mg-Fe alloys with low Si content, Metall. Mater. Trans. A Phys. Metall. Mater. Sci. 47 (2016) 1215–1228..


[13] SS-EN ISO 14577-1:2015, Metallic materials - Instrumented indentation test for hardness and materials parameters - Part 1: Test method, (2015).


[14] H.I. Laukli, C.M. Gourlay, A.K. Dahle, Migration of crystals during the filling of semi-solid castings, Metall. Mater. Trans. A Phys. Metall. Mater. Sci. 36 (2005) 805–818..


[15] J.A. Taylor, J. Barresi, M.J. Couper, D.H. StJohn, Influence of Mg content on the microstructure and solid solution chemistry of Al-7%Si-Mg casting alloys during solution treatment, in: Alum. Alloy. - Their Phys. Mech. Prop., Trans Tech Publications, 2000: p.277–282.


[16] ASTM B917/B917M-12 - Standard practice for heat treatment of aluminum-alloy castings from all processes, 1 (2012) 1–11..