Crystallisation characteristics of primary silicon particles in cast hypereutectic Al–Si alloy

Abstract

The crystallisation characteristics of primary silicon particles in a cast hypereutectic Al-Si alloy were examined using various casting processes. The size of the primary silicon particles depends on the cooling rate. However, the primary silicon particles cannot be crystallised completely when the cooling rate is .20 K s 21 , since uncrystallised Si atoms migrate to the regions at low cooling rates, producing large primary Si particles. Moreover, turbulent metal flow under conditions of high cooling rate leads to the macrosegregation of the primary Si particles, resulting in poor mechanical properties. From the crystallisation characteristics obtained, a suitable solidification criterion can be proposed.

Effect of Sr on Microstructures and Wear Properties in Sr-modified Hypoeutectic Al-Si-Cu-Mg Alloys

“…In particular, the microstructures of the samples with more than 200 ppm of Sr consisted of large primary Si with more finely dispersed eutectic Si, as shown in Figure 4,6. This finely dispersed eutectic Si in hypereutectic Al-Si alloys is typically required to obtain the best mechanical properties [3]. These hard and dispersed phases can improve surface hardness, which is one of the most important parameters determining abrasion resistance in abrasive wear [17].…”

“…The Al-Si-Cu-Mg alloys, especially when compared to Al-Si-Cu alloys, have demonstrated good wear resistance. However, their mechanical properties are significantly influenced by the size and morphology of the precipitated Si [3][4][5], making microstructural control a significant challenge. Various methods such as heat treatment, additives, and optimisation of casting techniques have been used as the primary means to control the Si phases in the microstructure.…”

Some Modern Methods of Improving the Properties of Hypereutectic Al–Si Alloys

“…Традиційно проблеми лиття таких стопів пов'язані з певними труднощами, реґулюванням розміру і розподілом первинної кремнійової фази і з високою теплотою топлення кремнію. Основним недоліком використання заевтектичних стопів Al-Si є утворення крупних частинок Si через низькі швидкості охолодження або погані умови тверднення [1, [6][7][8][9]. Наприклад, м'який Al швидко зношується (порівняно з набагато більш твердим Si), що приводить до «виходу» крупних частинок Si на поверхню [10].…”

Effect of heat treatment on microstructural characteristics and mechanical properties of hypereutectic B390 aluminium alloys modified by phosphorus and bismuth

“…In hypereutectic Al-Si-Cu-Mg alloys, the as-cast microstructure typically consists of primary Si, eutectic Si, intermetallic compounds, and an α-Al phase. However, the presence of large polygonal primary silicon and coarse eutectic silicon flakes was detected, resulting in a notable and adverse impact on both the mechanical characteristics and machinability of the hypereutectic Al-Si alloys [1,2]. Mechanical properties can be improved by microstructural modification.…”