Different Influences of Rare Earth Eu Addition on Primary Si Refinement in Hypereutectic Al–Si Alloys with Varied Purity

Abstract

The effect of alloying the Eu element on primary Si refinement in varied purity Al–16Si alloys was studied by scanning electron microscopy (SEM), thermal analysis, micro x–ray diffraction (μ–XRD), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). The results indicate that the P impurity element in hypereutectic Al–Si alloys has a great influence on the rare earths’ refinement efficiency of primary Si. Coinstantaneous primary Si refinement and eutectic Si modification by Eu was obtained in high purity (HP) Al–16Si and commercial purity (CP) Al–16Si–0.06P alloys, but the primary Si was gradually coarsened in CP Al–16Si alloys. An excellent integration of ultimate tensile strength (144.8 MPa) and elongation (9.8%) of CP hypereutectic Al–16Si–0.06P alloy was obtained by adding 0.15% Eu. The refinement of primary Si in Eu–modified HP Al–16Si alloys was related to the constitutional undercooling of Eu. There was no sufficient Eu element partition into the primary Si particles, and fewer parallel twins, rather than multiple twins, were observed within them. The refinement of primary Si in CP Al–16Si–0.06P alloys was caused by the overlay of two kinds of mechanisms including the heterogeneous nucleation mechanism of AlP and the constitutional supercooling mechanism of Eu. However, in order to refine the primary Si in CP hypereutectic Al–16Si alloys, the Eu:P weight ratio should not exceed 3.33, otherwise the refinement efficiency of primary Si will be reduced due to mutual poisoning between Eu and P. This work can be used to interpret the controversy concerning the influence of rare earths on the primary Si in hypereutectic Al–Si alloys, thereby elucidating the importance of alloy purity to primary Si refinement by rare earths.

Study of Si morphology in AlSi21CuNiMg cast alloy using col our and deep etching

“…The IIT mechanism suggests that the modifier atoms can adsorb on the growing planes {111} Si, thereby forming frequent multiple Si twins. It should be noted that either the suppression of the TPRE mechanism or the ITT mechanism may be related to the adsorption of modifier atoms in the Si phase [35].…”

Effect of Cooling Rate on Nano-Eutectic Formation in Laser Surface Remelted and Rare Earth Modified Hypereutectic Al-20Si Alloys

“…Chemical modification of the molten liquid has been examined to hinder Si segregation, by the addition of Na [11,12] and P [13,14]. Likewise, chemical modification by rare earth elements microalloying have been studied for Ce [15,16], Sr [5,17], Y [18,19], La [20], Eu [21,22], Yb [23] and Nd [24]. Chemical modification often leads to thermodynamically favorable phases other than primary Silicon, thereby reducing the degree of Si segregation.…”

Effect of Antimony on the Microstructure Evolution and Mechanical Properties of Hypereutectic Al–Si Rheological High Pressure Die Casting Alloy

“…In the traditional manufacturing process, the addition of refining or modifying elements to improve the microstructure of Al-Si alloys is commonly used because of its simple operation, high efficiency and low cost. 5,6 Phosphorus is generally used as a refining element for the PSPs in the hypereutectic Al-Si alloys. 7 Strontium or antimony is commonly used as a modifying element for the eutectic Si in hypoeutectic and eutectic Al-Si alloys.…”