Size Of Primary Si Particles Research Articles

Synergistic Effect of Strontium and Melt Quenching on the Solidification Microstructure of Hypereutectic Al-Si Alloys.

The synergistic effect between strontium (Sr) and melt quenching on the solidified microstructure of hypereutectic Al-Si alloys was investigated by optical and scanning electron microscopy. The results indicate that melt quenching can suppress the growth of primary Si particles in the solidified structure of the hypereutectic Al-Si alloy, resulting in a significant decrease of in the average size of primary Si particles in Al-(18~22)Si alloys from 30.35~66.31 μm to 15.13~34.63 μm. The synergistic effect between Sr and melt quenching can further inhibit the precipitation of primary Si particles in the Al-18Si alloy. After the addition of Sr to Al-18Si alloy and undergoing melt quenching, the area fraction of primary Si clearly decreases. When the added amount of Sr increases from 0.1 wt.% to 0.5 wt.%, the area fraction of primary Si decreases from 1.13% to 0.16%. With 0.5 wt.% Sr in the tested alloy, the inhibiting effect on primary Si precipitation was significantly improved. Research has shown that the cooling rate has a significant impact on the solidified structure of the melt-quenched Al-18Si-0.5Sr alloy. There exists no primary Si in solidified structures on the area of 1/8R and 1/4R from the surface of the round bar sample, but the area fraction of primary Si increases, respectively, to 1.97% and 12.48% on the area of 1/2R and R from the surface. The higher the cooling rate, the higher the inhibitory effect on the primary Si precipitation in the Al-18Si-0.5Sr alloy.

Effect of trace elements on the pinhole fatigue-resistance of gasoline Al-Si piston alloy

Trace elements, i.e., Cu, Ni, Zr and V are added into Al-Si piston alloy to optimize the phase structure. Micro-structures and fatigue performances are discussed. The stress state of pinhole inner-surface is investigated by finite element method (FEM). The comparative tests of original piston alloy and modified piston alloy are conducted on a specialized piston fatigue setup under the same condition as a real engine, and then the fracture analyses are addressed to discuss the relevant mechanisms. Results show the content and size of primary Si particles are restrained after the addition of trace elements. The ultimate tensile strength (UTS) and high cycle (HC) fatigue strength of modified piston alloys under high temperature are increased obviously. The increase of intermetallics and decrease of primary Si are the main reasons.

Effects of La–Ce addition on microstructure and mechanical properties of Al–18Si–4Cu–0.5Mg alloy

Abstract The microstructural evolution and mechanical properties of Al–18Si–4Cu–0.5Mg alloy modified by the addition of La–Ce rare earth elements through OM, SEM, EPMA and tensile tests were investigated. The results of OM and SEM analyses indicated that primary Si particles were significantly refined from coarse block-like and irregular polygonal shapes into fine flaky shapes, while eutectic Si particles were modified from coarse and needle-like into fine and rod- or coral-like shapes with increase of La–Ce addition. The alloy exhibited the minimum primary Si particle size and the best mechanical properties with the addition of 0.3 wt.% La–Ce. The average particle size decreased from 61 to 28 μm, the ultimate tensile strength increased from 222 to 242 MPa and the elongation increased from 3.2% to 6.3%. In addition, modification mechanisms and fracture modes were explored by the means of SEM and EPMA.

Effects of Heat Treatment on the Microstructures and High Temperature Mechanical Properties of Hypereutectic Al–14Si–Cu–Mg Alloy Manufactured by Liquid Phase Sintering Process

Hypereutectic Al–Si alloy is an aluminum alloy containing at least 12.6 wt.% Si. It is necessary to evenly control the primary Si particle size and distribution in hypereutectic Al–Si alloy. In order to achieve this, there have been attempts to manufacture hypereutectic Al–Si alloy through a liquid phase sintering. This study investigated the microstructures and high temperature mechanical properties of hypereutectic Al–14Si–Cu–Mg alloy manufactured by liquid phase sintering process and changes in them after T6 heat treatment. Microstructural observation identified large amounts of small primary Si particles evenly distributed in the matrix, and small amounts of various precipitation phases were found in grain interiors and grain boundaries. After T6 heat treatment, the primary Si particle size and shape did not change significantly, but the size and distribution of CuAl2 (θ) and AlCuMgSi (Q) changed. Hardness tests measured 97.36 HV after sintering and 142.5 HV after heat treatment. Compression tests were performed from room temperature to 300 °C. The results represented that yield strength was greater after heat treatment (RT ~ 300 °C: 351 ~ 93 MPa) than after sintering (RT ~ 300 °C: 210 ~ 89 MPa). Fracture surface analysis identified cracks developing mostly along the interface between the primary Si particles and the matrix with some differences among temperature conditions. In addition, brittle fracture mode was found after T6 heat treatment.

Effects of Process Parameters on Solidification Structure of A390 Aluminum Alloy Hollow Billet

The effects of process parameters on the solidification structure of A390 aluminum alloy hollow billets prepared by direct-chill casting were investigated. The decrease of casting temperature deteriorated the homogeneity and increased the size of primary Si particles in the hollow billet. Although the average size of primary Si particles was not obviously affected by the increase of casting speed, the thickness of Si-depleted layer at the inner wall increased with the higher casting speed. The tensile strength of A390 alloy is a function of the percentage of coarse Si particles (larger than 35 μm) and the average size of primary Si particles. Higher and more stable tensile strength can be received in the hollow billet with the casting temperature of 1050 K (777 °C), because the fine and uniformly distributed primary Si particles were obtained in the hollow billet.

The role of elevated temperature exposure on structural evolution and fatigue strength of eutectic AlSi12 alloys

Pistons of internal combustion (IC) engines are typically subjected during operation to high cycle fatigue loading at elevated temperatures (up to 350°C). The materials typically used for piston production are eutectic Al–Si alloys for their excellent fluidity and suitable mechanical properties. Results of a fatigue testing program of eutectic Al–Si alloys at room temperature and at elevated temperatures (250°C, 300°C and 350°C) performed with the aim to support piston design and material optimization are reported in this paper. Specimens were extracted from piston crowns and tested in a rotating bending test machine. The fatigue strength at 107cycles was quantified by a staircase approach.To investigate the strengthening mechanism based on the formation of precipitates (Guinier–Preston (GP) zones) during decomposition of a metastable supersaturated solid solution, a structural investigation of one of the alloys before and after fatigue testing at elevated temperatures was conducted. Metallography, color etching, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to elucidate the following aspects: (1) the structural features of the alloy (dendrites of α-phase, primary Si particle size and distribution, morphology and distribution of intermetallic phases); (2) the changes of the strengthening mechanism (GP zones) with elevated temperature exposure.

Fatigue Strength Degradation of AlSi12CuNiMg Alloy Due to High Temperature Exposure: A Structural Investigation

The strengthening mechanism based on the formation of precipitates (Guinier-Preston (GP) zones) during decomposition of a metastable supersaturated solid solution is stable and effective below temperatures, which are typically overcome in the piston region facing the combustion chamber. Therefore, pistons experience a progressive loss of strength due to over-aging during service. This contribution reports of a structural investigation on a eutectic AlSi12CuNiMg alloy before and after fatigue testing at high temperatures (up to 350°C). Metallography, color etching, SEM and TEM are used to elucidate the following aspects: 1) the structural features of the alloy (dendrites of α−phase, primary Si particle size and distribution, morphology and distribution of intermetallic phases); 2) the evolution of the strengthening mechanism (GP zones) with high temperature exposure.

Refinement of the primary Si particles in hypereutectic aluminum alloy

Al-Si alloys, with such excellent properties as low weight, low thermal expansion coefficient, and high wear-resistance, are ideal materials for the automobile and aerospace industries. However, their applications have been hampered by the coarsening of the primary-Si particles in Al-Si alloys. In this study, simple plastic deformation was used to reduce primary-Si particles and to improve the wear-resistance and mechanical strength of Al-Si alloys. Experimental results showed that mechanical rolling decreased the grain size of primary-Si particles in Al-Si alloys and reduced the variation in silicon particle size. After 60%-roll-reduction, the alloy showed an improved tensile strength of 340 MPa, which is attributed to the work hardening of the aluminum matrix and the dispersion strengthening of the primary-Si particles. Data from wear-resistance testing showed that rolling led to a reduction in wear loss. This improvement in wear resistance is due to the particle size refinement of silicon at a high percentage-roll-reduction.

ULTRAFINE PRIMARY SILICON PARTICLES IN PHOSPHORUS-MODIFIED HYPEREUTECTIC AL-SI ALLOY POWDERS PRODUCED BY SAMD METHOD

In the present study, alloy powder batches of Al-20Si (wt. %) were generated by SAMD technique using NaCl as the solid media. The method consists of introducing and mixing a specified amount of NaCl particles (mean diameter 254 μm) in aluminum melt at the temperature of 710°C. Melt disintegration occurs in 5 min by kinetic energy transfer from a rotating impeller (1400 rpm) to the metal via the solid atomizing medium ( NaCl particles). The resulting mixture of aluminum droplets and NaCl particles are subsequently quenched in water to dissolve NaCl and solidify Al droplets to produce powder particles. In order to investigate the effect of phosphorus modification on the size and morphology of the primary Si particles, the SAMD technique was also performed to produce Al-20Si -0.015P powder particles. The resultant powders were screened through 6 different sized sieves ranging from 38 to 500 μm and different powder fractions were cold mounted, polished and studied by optical microscopy. It was concluded that for both un-modified and modified alloys, there was a decrease in the size of primary Si particles corresponding to a decrease in the powder particle size. However, the same sized phosphorus modified powders exhibited considerably finer primary Si particles in which the average size of these ultrafine Si particles was about 1.1 μm for the smallest sieved particles.

가스분무 공정에 의한 고강도 과공정 Al-Si 합금 분말의 제조 및 특성 연구 I. 분말 제조 및 성형성

In order to improve mechanical properties, the hypereutectic Al-20 wt%Si based prealloy powder was prepared by gas atomization process. Microstructure and compressibility of the atomized Al-Si powder were investigated. The average powder size was decreased with increasing the atomization gas pressure. Size of primary Si particles of the as-atomized powder was about <TEX>$5-8\;\mu{m}$</TEX>. The as-atomized Al-Si powder such as AMB 2712 and AMB 7775 to increase compressibility and sinterability. Relative density of the mixed powder samples sintered at <TEX>$600^{\circ}C$</TEX> was reached about 96% of a theoretical density.

Enhanced Modification Process of B.390 Casting Alloy by the Ca Content Control

Primary Si particle size has been refined as Ca content of the melts decreased and cooling rate increased. A control of Ca content by the addition of CuCl2 to the melt was the most efficient in the refinement of primary Si particles. The minimum size of primary Si particles in this study was 15.0um when a residual content of Ca element in the alloy was 5ppm. Primary Si particle size was refined as primary Si crystallization temperature increased, which was attributed to the decrease of Ca content in the melts.

Improvement in wear resistance of hyper-eutectic AlSi cast alloy by laser surface remelting

Laser surface remelting of hyper-eutectic Al20 and 30 mass%Si cast alloys with CO 2 laser beam has been fined to improve the wear resistance of these alloys. A continuous wave CO 2 laser beam with the power of 5kW was irradiated on these AlSi cast alloy substrates under various defocused distance of laser beam with the argon gas shielding. The microstructure of the laser-remelted layer consisted of fine primary Si particles, primary α-Al matrix phase and fine α-AlSi eutectic phase. The size of the primary Si particle decreased from 25 to 3 μm with the defocused distance also decreasing. Fine primary Si particles were distributed uniformly in the matrix of the fully remelted layer. The hardness of the laser remelted layer increased gradually with the decrease of the primary Si particle size, which reached 140 HV at about 5 μm in Al30 mass%Si layer. The wear resistance of the remelted layer increased with increasing the hardness and decreasing the size of primary Si particle. The wear resistance of the remelted layer in Al30 mass%Si cast alloy was better than that of the Al20 mass%Si cast alloy.

Sliding wear behavior of some Al-Si alloys: Role of shape and size of Si particles and test conditions

In this investigation, effects of the shape and size of silicon particles have been studied on the sliding wear response of two Al-Si alloys, namely, LM13 and LM29. The LM13 alloy comprised 11.70 pct Si, 1.02 pct Cu, 1.50 pct Ni, 1.08 pct Mg, 0.70 pct Fe, 0.80 pct Mn, and remainder Al. The LM29 alloy contained 23.25 pct Si, 0.80 pct Cu, 1.10 pct Ni, 1.21 pct Mg, 0.71 pct Fe, 0.61 pct Mn, and remainder Al. Wear tests were conducted under the conditions of varying sliding speed and applied pressure. The alloys were also characterized for their microstructural features and mechanical properties. The presence of primary silicon particles in the alloy led to a higher hardness but lower tensile properties. Further, refinement in the size of the primary particles improved the mechanical properties of the alloy system. The wear behavior of the alloys was influenced by the presence of primary Si particles and was a function of their size. Samples with refined but identical microconstituents (e.g., pressure cast vs gravity cast LM29 in terms of the size of primary Si particles and dendritic arm spacing) exhibited better wear characteristics. Their overall effect was further controlled by the test conditions. It was observed that test conditions leading to the generation of an optimal degree of frictional heating offer the best wear resistance. This was attributed to the reduced microcracking tendency of the alloy system otherwise introduced by the Si particles. The reduced microcracking tendency in turn allows the Si phase to carry load more effectively and impart better thermal stability to the alloy system. This caused improved wear resistance under the circumstances. Further, the primary Si particles improved the wear resistance of the alloy system (e.g., gravity-cast LM29 vs gravity-cast LM13) under high operating temperature conditions. Additional thermal stability and protection offered to the matrix by the primary Si phase, under the conditions of reduced microcracking tendency, were the reasons for the improved wear characteristics of the alloy system. Conversely, a reverse effect was produced at low operating temperatures in view of the predominating microcracking tendency. The study suggests that shape, size, microcracking tendency, and thermal stability of different microconstituents greatly control the mechanical and tribological properties of these alloys. The extent of effective load transfer between the phases plays an important role in this regard. Further, the overall effect of these factors is significantly governed by the test conditions.

発光分析による過共晶Ａｌ‐Ｓｉ系合金中のけい素の定量に及ぼす初晶けい素粒径の影響

発光分析による過共晶Ａｌ‐Ｓｉ系合金中のけい素の定量に及ぼす初晶けい素粒径の影響