The Effect of Cooling Rate on Properties of Intermetallic Phase in a Complex Al-Si Alloy

Abstract

The cooling rate is one of the main tools available to the process engineer by means of which it is possible to influence the crystallisation process. Imposing a desired microstructure on a casting as early as in the casting solidification phase widens significantly the scope of technological options at disposal in the process of aluminium-silicon alloy parts design and application. By changing the cooling rate it is possible to influence the course of the crystallisation process and thus also the material properties of individual microstructure components. In the study reported in this paper it has been found that the increase of cooling rate within the range of solidification temperatures of a complex aluminium-silicon alloy resulted in a decrease of values of the instrumented indentation hardness (H IT ) and the instrumented indentation elastic modulus (E IT ) characterising the intermetallic phase occurring in the form of polygons, rich in aluminium, iron, silicon, manganese, and chromium, containing also copper, nickel, and vanadium. Increased cooling rate resulted in supersaturation of the matrix with alloying elements.

Role of Chemical Composition in Corrosion of Aluminum Alloys

“…The increasing content of Fe leads to formation of, especially, iron-rich phases in form of needles, then it in forms into skeleton-like shapes. Skeleton-like shapes were not observed in alloys B and C. These findings correlate with research work of authors [12][13][14]. The authors confirmed that the higher the iron content, the longer and wider the needles.…”

“…Most negative are iron-rich intermetallic phases. In Fe-containing aluminum cast alloys, Fe-rich intermetallic phases are formed, such as β-Al [12][13][14][15]. The Chinese script morphology of the α-iron phase occurs during eutectic solidification.…”

“…From electrochemical point of view, the β-Al 5 FeSi phase is nobler than the matrix in aqueous media, making the alloy system highly susceptible to localized corrosion. The harmful effect of the β-iron phase can be neutralized by rapid solidification; addition of neutralizers such as Mn, Co., Cr, Ni, Sr, K, and Be can change the morphology of the phases or enhance the precipitation of Fe-rich particles, which are less harmful than needles; melt superheat; strontium modification and non-equilibrium solution heat treatment [1,[12][13][14]27,28]. Observation of the basic microstructure of all experimental materials showed that it consists of α-phase dendrites, eutectic (a mechanical mixture of α-phase and eutectic silicon) and different intermetallic phases (Figures 2 and 3).…”

“…In Fe-containing aluminum cast alloys, Fe-rich intermetallic phases are formed, such as β-Al5FeSi; Al9FeSi2, Al3FeSi2, Al4FeSi2, α-Al15(FeMn)3Si2, Al8Fe2Si, Al19Fe4MnSi, Al12MnSi2, Al12Fe3Si, π-Al8Mg3FeSi6, and Al5Si6Mg8Fe2. From these phases identified in Al-Si base alloys, the α-Al15FeMn3Si2 and β-Al5FeSi phases are more important [12][13][14][15]. The Chinese script morphology of the α-iron phase occurs during eutectic solidification.…”

Layered Double Hydroxide Protective Films Developed on Aluminum and Aluminum Alloys: Synthetic Methods and Anti-Corrosion Mechanisms

“…Several intermetallic phase particles, like Al 3 Mg 2 , Mg 2 Si, Al 2 CuMg, and MgZn 2 are anodic to the aluminum matrix and corrode preferentially with respect to the aluminum matrix, while the particles like AlFeMnSi, AlCuFeMn, Al 2 Cu (θ phase) and AlCuFeSi are found to be cathodic with respect to the aluminum matrix and cause peripheral trenches in the aluminum matrix adjacent to the intermetallic particles [7]. Iron, which is major class of secondary phase (AlFe and/or AlFeSi), induces a decrease of both mechanical and corrosion resistance properties but it reduces the tendency to adhere to metal molds [8]. The anodic behavior of intermetallic particles regarding the aluminum matrix can cause localized corrosion [9].…”