Microindentation Hardness-Secondary Dendritic Spacings Correlation with Casting Thermal Parameters in an Al-9wt.%Si Alloy

Abstract

Experiments were carried out to analyze the effect of growth rates (VL) and cooling rates (TR) on both secondary dendritic arm spacings (λ2) and Vickers microhardness (HV) of an Al-9wt.%Si alloy during the horizontal directional solidification under transient heat flow conditions. A water-cooled solidification experimental apparatus was developed allowing a wide range of TR (from 0.2 to 3.5 ºC/s) to be experienced. Five computer guided thermocouples were connected with the metal, and the time-temperature data were recorded automatically. The solidification path was also calculated by Scheil model in Thermo-Calc software. Casting samples were characterized by the combined analyses of optical microscopy (OM) and scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS) revealing a complex arrangement of phases including α-Al dendrites, Si particles and Fe-rich phases within interdendritic regions. It was observed that power law functions characterize the variation of λ2 as a function of VL and TR with exponents of-2/3 and-1/3, respectively. Finally, experimental laws of power and Hall-Petch types are proposed relating the resulting HV to the λ2. According to these results, it was found that, for increasing values of λ2, the results of HV decrease.

Microstructure and Microhardness of Directionally Solidified Al-Si Alloys Subjected to an Equal-Channel Angular Pressing Process

“…In that figure, the dashed curves come from experimental functions that were fitted to the experimental data. As can be seen, in both cases λ 2 is affected by Ṫ, which is evidenced by the 34 and Carvalho et al 35 ) and show the effect of Ṫ on λ 2 . This effect translates to the microstructure growth, i.e., high values of Ṫ near the mold bottom favor a more refined microstructure, whereas low values of this thermal parameter close to the top of the castings contribute effectively to yield a coarser microstructure.…”

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

“…Brito et al [53] (Al-3 wt%Mg alloy) and Spinelli et al [54] (hypoeutectic Al-Cu alloys, including the Al-3 wt%Cu alloy) have also proposed a -2/3 power law to represent the k 2 variation with G R for downward directionally solidified samples. Likewise, Costa et al [27] and Carvalho et al [55] have found exponential equations of the form k 2 = constant (C R ) -1/3 to correlate k 2 with C R for horizontally solidified Al-6 wt%Cu and Al-9 wt%Si alloys, respectively.…”

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

“…, whose exponent (-2/3) has been validated by several experimental investigations on unsteady-state directional solidification of aluminum-based binary and multicomponent alloys, for both horizontal and vertical directions 2,16,17,23,[25][26][27][28]38,39 . Among the works on transient solidification, it is emphasized those reported for binary Al-Si 2,38,39 and multicomponent Al-Si-(Cu and Mg) 23,[25][26][27][28]30 alloys.…”

“…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.…”