Interconnection between microstructure and microhardness of directionally solidified binary Al-6wt.%Cu and multicomponent Al-6wt.%Cu-8wt.%Si alloys

Abstract

An experimental study has been carried out to evaluate the microstructural and microhardness evolution on the directionally solidifi ed binary Al-Cu and multicomponent Al-Cu-Si alloys and the infl uence of Si alloying. For this purpose specimens of Al-6wt.%Cu and Al-6wt.%Cu-8wt.%Si alloys were prepared and directionally solidifi ed under transient conditions of heat extraction. A water-cooled horizontal directional solidifi cation device was applied. A comprehensive characterization is performed including experimental dendrite tip growth rates (V L ) and cooling rates (T R ) by measuring Vickers microhardness (HV), optical microscopy and scanning electron microscopy with microanalysis performed by energy dispersive spectrometry (SEM-EDS). The results show, for both studied alloys, the increasing of T R and V L reduced the primary dendrite arm spacing (λ 1 ) increasing the microhardness. Furthermore, the incorporation of Si in Al-6wt.%Cu alloy to form the Al-6wt.%Cu-8wt.%Si alloy infl uenced signifi cantly the microstructure and consequently the microhardness but did not affect the primary dendritic growth law. An analysis on the formation of the columnar to equiaxed transition (CET) is also performed and the results show that the occurrence of CET is not sharp, i.e., the CET in both cases occurs in a zone rather than in a parallel plane to the chill wall, where both columnar and equiaxed grains are be able to exist.

Microstructure and microhardness in horizontally solidified Al–7Si–0.15Fe–(3Cu; 0.3Mg) alloys

“…The main reason is that in the case of vertical upward DS, the effect of convection flows can be minimised, promoting a better stability to the solidification process. On the other hand, when the chill is placed on the side of the mould (horizontal DS), convection flow as a function of both thermal and composition gradients in the liquid occurs [35][36][37][38]. As a consequence, the microstructural development during the transient horizontal directional solidification (THDS) of Al-Si-(Cu, Mg) alloys may be considered as a complex and interesting phenomenon to be studied.…”

Horizontally Solidified Al–3 wt%Cu–(0.5 wt%Mg) Alloys: Tailoring Thermal Parameters, Microstructure, Microhardness, and Corrosion Behavior

“…Additionally, Dias Filho et al [28] have shown that the k 3 evolution of the same Al-Cu alloy during unsteady-state horizontal solidification may also be related to G R and C R by -1.1 and -0.55 power laws, respectively. In the study by Vasconcelos et al [29], the microhardness (HV) dependence on microstructural features of a horizontally solidified Al-6 wt%Cu alloy has been evaluated using power and Hall-Petch-type experimental equation. In a recent investigation, Kaygısız and Marasli [30] analyzed samples of a eutectic Al-30 wt%Cu-6 wt%Mg alloy solidified in a Bridgman-type upward solidification furnace and have proposed experimental equations to represent the functional dependencies of lamellar eutectic spacings (k E ) of both Al 2 CuMg and Al 2 Cu phases, HV profile, tensile strength (r T ), and electrical resistivity (q) on G R .…”

Relationship Between Aluminum-Rich/Intermetallic Phases and Microhardness of a Horizontally Solidified AlSiMgFe Alloy

“…It is observed that higher HV values were obtained in the interdendritic regions, in which Si + π + θ particles of high hardness are present. Vasconcelos et al 48 , Araújo et al 28 and Souza et al 40 have found higher HV values for Al-Si multicomponent alloys with addition of Cu and Mg and the authors have attributed to the presence of intermetallic phases (Al 2 Cu and Mg 2 Si) of high hardness in the interdendritic region of the as-solidified samples. In contrast to the procedure adopted in the present study, these authors did not perform HV measurements in the Al-rich and eutectic phases, the HV values reported by them were the means of 20 measurements obtained directly in the casting samples.…”

“…The dependence of the microhardness (HV) on the microstructure in Al-based binary and multicomponent alloys has been investigated for several directional solidification systems 23,28,38,[41][42][43][44][45][46][47][48] and the results obtained in these studies have shown that power and Hall-Petch types experimental equations may characterize the variation of HV with λ 1 , λ 2 and λ 3 , of which the alloys containing the Si as the major alloying element with Cu/Mg/Sn addition are highlighted. This can be seen in Table 1.…”