Effect of phosphorus and heat treatment on microstructure of Al-25%Si alloy

Abstract

T he hypereutectic Al-Si alloys play an important role in the fields of automotive and aerospace industries due to their excellent casting ability, low thermal expansion coefficient and high wear resistance [1][2][3] . The microstructure evolution of hypereutectic Al-Si alloy is mainly divided into two stages during solidification: the precipitation of primary silicon and subsequent eutectic transformation. The morphology and distribution of silicon affect the mechanical properties and application scope of the alloys. For hypereutectic Al-Si alloys, the coarse primary silicon may easily produce stress concentration, form the crack and accelerate the crack growth. To gain better mechanical properties, modification treatment and heat treatment are carried out for hypereutectic Al-Si alloys to change the morphology, size and distribution of silicon phase. Modification treatment can significantly improve the morphology and distribution of silicon [4][5][6][7][8][9] . Heat treatment aims at acquisitions of supersaturated solution, high density vacancies and spheroidization of eutectic Si. Many researchers have focused on the improvement of modifiers to meet the requirements of environmental protection and industry applications. The common methods of modification are chemical treatment by modifiers [5][6][7][8][9] , melt thermal treatment [10][11][12] and Abstract: It is known that phosphorus can refine the primary silicon and heat treatment can spheroidize the eutectic silicon. This paper presents an optimal combination of heat treatment processes and P refinement on hypereutectic Al-Si alloy. The optimal P addition amount, and the solution and aging temperatures for Al-25%Si alloy were obtained through the orthogonal experiment, and their modification effects were discussed. The results show that P addition has the greatest modification effect, followed by aging temperature, and the modification effect of solution temperature is the least. The optimized modification parameters are: addition of 0.6% P, solution at 540 ºC and aging at 160 ºC . In addition, the cooling curve, superheating and hardness of the alloy were also analyzed. mechanical/electromagnetic stirring treatment [13][14][15] . Key words:Refinement by element addition has been widely applied in traditional casting Al-Si alloy due to simplicity and validity [4][5][6][7][8][9] . P is one of the most effective modifiers and refiners of primary Si particles and can be added into the melt as master alloys, such as Si-P [5] , Cu-P [6] , Al-P [7] , Al-Si-P [8] and Al-Zr-P [9] . Adding P to Al-Si hypereutectic alloy can reduce the size of primary Si particles by the active nuclei sites [16] . Wu Yaping found the best modification effect can be achieved when Si-P master alloy is added into Al melt before the addition of silicon instead of directly adding into Al-24%Si alloy melt, because AlP can form after adding the Si-P into Al melt which can act as the nuclei of primary Si phases during the solidification process. The optimized modification parameters were mo...

Tribology of Si-rich TIG-deposited coatings on Zn–40Al–2Cu alloy

“…Their EDS analyses are presented in Table 2. As seen, due to the very low solid-solubility in Zn-Al matrix [4], Si atoms almost entirely precipitate as pure Si. The higher the Si concentration is, the higher the size and volume fraction of Si particles, especially the irregular-shaped primary particles.…”

“…Regarding the general similarity between the size and morphology of Si P particles in Zn-40Al-2Cu and hypereutectic Al-Si alloys, different techniques can be used to modify the shape and distribution of Si P particles in the microstructure of Zn-40Al-2Cu alloy, the most important of which are heat treatment [4], rapid solidification [5,6], mechanical/thermo-mechanical processing [7][8][9], chemical modification [4,[10][11][12], and molten metal processing [13][14][15]. Some techniques are cost-intensive and need special equipment.…”

Intermetallics Formation and Their Effect on Mechanical Properties of Al-Si-X Alloys

“…β-phase morphology is platelet-like (needlelike) appearance and serves as a stress-raiser in the matrix, while α-Phase morphology is like polyhedral crystals and sometimes like Chinese script. The detrimental effects of intermetallic need to be removed or reduced; some of the techniques that are exploited include thermal treatment, chemical solutions and microstructural control by co-injecting inoculated intermetallic particles [54][55][56].…”

Study on the Anti-Poison Performance of Al–Y–P Master Alloy for Impurity Ca in Aluminum Alloys

“…This was attributed to the presence of AlP, which could act as the ideal heterogeneous nucleation sites of Si phase due to the very similar lattice parameters [ 18 ]. Up to now, types of master alloys containing phosphorus have been designed to meet the requirement of industry applications, including Cu–P [ 19 ], Al–P [ 3 , 20 ], Al–Cu–P, Al–Fe–P [ 21 ], Al–Si–P [ 22 ], Al–Zr–P [ 23 ], Al–RE–P [ 24 ], and so on. Among these master alloys, novel Al–6Y–2P master alloy containing YP particles has drawn much attention for the excellent composite modification performance for hypereutectic Al–Si alloys.…”