Influence of melt treatments and polished CVD diamond coated insert on cutting force and surface integrity in turning of Al-7Si and Al-7Si-2.5Cu cast alloys

The microstructures, machinability and surface characteristics of Al-7Si and Al-7Si-2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. The results indicate that combined grain refined and modified Al-7Si-2.5Cu cast alloys have microstructures consisting of uniformly distributed α-Al grains, eutectic Al-silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better machinability and surface characteristics in the cast condition compared with the same alloy subjected to only grain refinement or modification. Performances of the turning inserts (uncoated and polished CVD diamond coated) were evaluated in machining Al-7Si and Al-7Si-2.5Cu cast alloys under dry environment using a lathe. The polished CVD diamond coated insert outperformed the uncoated cutting insert which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The polished CVD diamond coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate the influence of grain refinement, modification and combined action of both on the microstructural changes in the Al-7Si and Al-7Si-2.5Cu cast alloys and their machinability and surface finish when different turning inserts are used.     

Influence of melt treatments on sliding wear behavior of Al–7Si and Al–7Si–2.5Cu cast alloys

The microstructures and dry sliding wear behavior of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al–7Si–2.5Cu cast alloys have microstructures consisting of uniformly distributed α-Al grains, eutectic Al– silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better wear resistance in the cast condition compared with the same alloy subjected to only grain refinement or modification. The improved wear resistances of Al–7Si–2.5Cu cast alloys are related to the refinement of the aluminum grain size, uniform distribution of eutectic Al-silicon and fine CuAl₂ particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate the influence of the microstructural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys by grain refinement, modification and combined action of both on the sliding wear behavior.     

Influence of melt treatments and turning inserts on cutting force and surface integrity in turning of Al–7Si and Al–7Si–2.5Cu cast alloys

The microstructures, machinability and surface characteristics of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al–7Si–2.5Cu cast alloys have microstructures consisting of uniformly distributed α-Al grains, eutectic Al–silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better machinability and surface characteristics in the cast condition compared with the same alloy subjected to only grain refinement or modification. Performances of the turning inserts (Un-coated, PVD and Polished CVD diamond coated) were evaluated in machining Al–7Si and Al–7Si–2.5Cu cast alloys under dry environment using a lathe. The Polished CVD diamond coated insert outperformed the Un-coated or PVD-coated cutting inserts which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The Polished CVD diamond coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate the influence of grain refinement, modification and combined action of both on the microstrutural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys and their machinability and surface finish when different turning inserts used.     

Impact toughness in Al–12Si and Al–12Si–3Cu cast alloys—Part 1: Effect of process variables and microstructure

The charpy impact energy of Al–12Si and Al–12Si–3Cu cast alloys was measured in terms of the total absorbed energy. The standard charpy specimens 10×10×55 mm with a 2 mm V-notch were prepared from the castings. Effect of process variables and microstructural changes on the impact toughness of Al–12Si and Al–12Si–3Cu cast alloys was investigated. The results indicate that combined grain refined and modified Al–12Si–3Cu cast alloys have microstructures consisting of uniformly distributed α-Al dendrites, eutectic Al–Si and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better impact toughness in the cast condition compared with the same alloy subjected to only grain refinement or modification.     

Influence of rotational speed during centrifugal casting on sliding wear behaviour of the Al-2Si alloy

The microstructures and dry sliding wear behaviour of an Al-2Si alloy cast centrifugally are studied. Results indicate that at optimum speed the cast has a microstructure consisting of uniformly distributed α-Al grains and fine eutectic silicon grains. The cast exhibited better wear resistance compared to the same cast prepared at different rpms. This paper attempts to investigate the influence of the microstructural changes in the Al-2Si alloy by varying the rotational speed of the mould and its combined action on the dry sliding wear behaviour.     

Structure and mechanical Properties of Al-40% Cu Directionally Solidified Alloy

Commercial purity Al-40% Cu alloys were directionally solidified under a constant temperature gradient of 9 K/mm and growth rate (R) varying from 8 to 305 μm/sec. Cellular structure was obtained with a single primary CuAl₂ rod-like dendrite in the cell centre and a fanned-out eutectic structure surrounding it, while the boundary was composed of a coarser eutectic structure. The intercellular spacing and/or the CuAl₂ interdendritic spacing varied with (R)^?1/3. The UTS increased with R and was found to be lower than that of Al? CuAl₂ eutectics grown under similar conditions. The fracture strength of the primary CuAl₂ dendrites was calculated and was found to increase with decreasing their cross-sectional area.     

Effect of Al-5Ti-1B on the microstructure of near-eutectic Al-13.0%Si alloys modified with Sr

The addition of Sr in Al-Si alloys as a modifier causes a transition of the morphology of eutectic silicon from coarse plate-like or acicular to fine fibrous. However, it may also lead to the formation of long columnar dendritic -Al phase. Al-5Ti-1B master alloy is often used as a grain refiner to achieve the fine equaixed grains in aluminum and aluminum alloys. The aim of the present study is to highlight the effect of Al-5Ti-1B master alloy additions on the microstructure of near-eutectic Al-Si alloys modified with Sr. When the addition of Al-5Ti-1B master alloy was below 0.82 mass%, the dendritic -Al phase changed from long columnar to equiaxed, and there were no noticeable changes of the morphology and size of eutectic silicon, while the size of eutectic cells decreased slightly. However, when the addition was above 0.82 mass%, the deleterious influence of Al-5Ti-1B master alloy on the modification effect of Sr emerged and with further increases in addition level a fully unmodified microstructure was finally produced. The results indicate that the effective Sr in the melt decreases with increased addition of Al-5Ti-1B. The poisoning event of Al-5Ti-1B master alloy on the modification of Sr is supposed to be related with the interaction between Sr and Ti.     

Microstructural,mechanical and tribological properties of Al–7Si–(0–5)Zn alloys

A series of Al–7Si–(0–5)Zn alloys were produced by permanent mould casting and their microstructure, mechanical and tribological properties were investigated in as-cast state. The microstructure of Al–7Si alloy consisted of α-Al dendrites surrounded by eutectic Al–Si mixture and a small amount of primary silicon particles. Addition of zinc into Al–7Si alloy resulted in the formation of α-solid solution and an increase in size and volume fraction of primary silicon particles. Moreover, these particles gathered inside interdendritic regions of the ternary Al–7Si–Zn alloys. The density, strength and hardness of Al–7Si–Zn alloys increased continuously with increasing zinc content, but their elongation to fracture and impact energy showed a reverse trend. It was also observed that zinc had no significant effect on the friction coefficient of the alloys, but their wear volume decreased with increasing zinc content up to 4%, above which the trend reversed. The wear surfaces of the alloys were characterized mainly by smearing layer with some degree of oxidation. In addition, delamination and fine scratches were observed on the worn surface. It was concluded that the addition of zinc up to 4% improves both mechanical and wear behaviour of Al–7Si alloy.     

新型Al-12．7Si-0．7Mg焊丝及其熔敷金属组织与性能研究

借助OM、SEM、TEM和拉伸实验机,研究了新型Al-12．7Si—0．7Mg焊丝及其熔敷金属的组织和性能,结果表明：密集排布的针片状Si相经热挤压和连续冷拉拔后破碎为细小颗粒并弥散分布,当拉拔变形量为77％时,焊丝的组织和拉伸性能较优,经固溶和时效热处理后焊丝熔敷金属拉伸性能显著提高,Al-12．7Si—0．7Mg焊丝合金可热处理强化。     

Effect of mischmetal modification treatment on the microstructure,tensile properties,and fracture behavior of Al-7.0%Si-0.3%Mg foundry aluminum alloys

The influence of 0.1–1.0 wt% mischmetal (MM) additives on the microstructures, tensile properties, and fracture behavior of A356 alloys were investigated in detail under the as-cast condition. Experimental results show that, after introducing a small amount of MM, grain coarsening occurred, the eutectic silicon was well modified, and RE-containing intermetallic compounds containing Al, Si, Mg, La, and Ce elements were formed. The size, shape, and distribution of RE-containing compounds are also studied. Tensile tests revealed that MM addition decreases the tensile strength and ductility of the materials. The fracture path goes through the interdendritic regions containing eutectic silicon and RE-containing compounds.     

Influences of Preparation Conditions and Melt Treatment Procedureson Melt Treatment Performance of Al-5Ti-Band Al-10Sr Master Alloys

The influences of preparation conditions of Al-5Ti-B （as-cast and hot-rolled） and Al-10Sr （as-cast and hotextruded） and melt treatment procedures on the grain refinement and modification performance of A356 alloy are experimentally studied. For the two master alloys, the 50% reduction is sufficient to meet the demands of the efficient grain refinement and modification of A356 alloy. When Al-STi-B is introduced into the melt prior to degassing, the grain refinement efficiency of Al-5Ti-B will be greatly increased due to the better dispersity of TiB2 particles. Al-5Ti-B master alloy is less prone to affect the modification effect of Al-10Sr when they are used together.     

Effects of calcium on the microstructures and tensile properties of Mg-5Li-3Al alloys

The as-cast Mg-5Li-3Al-xCa (x = 0, 0.5, 1, 1.5 wt.%) was prepared with vacuum induction melting furnace, then processed by hot extrusion. The microstructures and tensile properties were investigated. The results show that the grains of as-cast alloys were refined gradually with the increase of Ca content from 0.5 wt.% to 1 wt.%, while the Ca content increases to 1.5 wt.%, the grain size increases. The microstructures of investigated alloys were further refined after hot extrusion. Both as-cast and as-extruded Mg-5Li-3Al-0.5Ca alloys have the highest mechanical properties, which is mainly attributed to the grain refinement caused by the addition of Ca and the formation of strengthening phase, Al₄Ca. When the addition of Ca is up to 1-1.5 wt.%, the tensile properties of alloys are worsened due to the excessive (Mg, Al)₂Ca eutectic phase forming at grain boundary.     

Effect of Cu addition on microstructures and tensile properties of high-pressure die-casting Al-5.5Mg-0.7Mn alloy

In this study, Cu was added into the high-pressure die-casting Al-5.5Mg-0.7Mn (wt%) alloy to improve the tensile properties. The effects of Cu addition on the microstructures, mechanical properties of the Al-5.5Mg-0.7Mn alloys under both as-cast and T5 treatment conditions have been investigated. Additions of 0.5 wt%, 0.8 wt% and 1.5 wt% Cu can lead to the formation of irregular-shaped Al₂CuMg particles distributed along the grain boundaries in the as-cast alloys. Furthermore, the rest of Cu can dissolve into the matrixes. The lath-shaped Al₂CuMg precipitates with a size of 15–20 nm × 2–4 nm were generated in the T5-treated Al-5.5Mg-0.7Mn-xCu (x = 0.5, 0.8, 1.5 wt%) alloys. The room temperature tensile and yield strengths of alloys increase with increasing the content of Cu. Increasing Cu content results in more Al₂CuMg phase formation along the grain boundaries, which causes more cracks during tensile deformation and lower ductility. Al-5.5Mg-0.7Mn-0.8Cu alloy exhibits excellent comprehensive tensile properties under both as-cast and T5-treated conditions. The yield strength of 179 MPa, the ultimate tensile strength of 303 MPa and the elongation of 8.7% were achieved in the as-cast Al-5.5Mg-0.7Mn-0.8Cu alloy, while the yield strength significantly was improved to 198 MPa after T5 treatment.     

Influence of Solution Temperature on Microstructure and Mechanical Properties of Two Cast Al-Si Alloys

In the present paper the influence of solution temperature 450-550°C on microstructure and mechanical properties of cast Al-12%-0.3% Mg and Al-16%-0.3% Mg alloys has been reported. It was observed that an increase in solution temperature increased the tensile strength of all alloys under investigation. Ductility was adversely affected. Higher solution temperature produced better refinement and distribution of eutectic silicon crystals than a low temperature. Heat treatment of all alloys showed spheroidization of eutectic silicon crystals. Scanning electron microscopy (SEM) of tensile-fractured surfaces was carried out to investigate the influence of solution temperature on the mode of fracture.     

Effect of silicon content in grain refining hypoeutectic Al–Si foundry alloys with boron and titanium additions

Abstract

The effect of Si content on the grain refinement of hypoeutectic Al–Si alloys was investigated. Alloying with Si refines the grain structure, which tends to be coarse and columnar in commercially pure aluminium. The smallest grain size occurs at ～2 wt-%Si, where the solidification interval of hypoeutectic Al–Si alloys is the largest. Grains become increasingly coarser with increasing Si starting from this point. The grains of Al–Si alloys with 500 ppm Ti are smaller than those cast without Ti regardless of the Si content of the alloy. The fivefold reduction in grain size in commercially pure aluminium upon Ti addition is gradually reduced with increasing Si. Finally, the grain refinement provided by Ti fails to meet the expectations once Ti starts to be removed from the melt via the formation of Ti–Si compounds above 5 wt-%Si. The B addition relies on the formation of AlB₂ particles to offer grain refinement. Analysis of the Al rich corner of the calculated Al–Si–B liquidus surface suggests that the primary AlB₂ is formed at a Si concentration of ～4 wt-%. While a perfect grain refiner for hypoeutectic Al–Si alloys with at least 4 wt-%Si, B fails to refine the grain structure when the Si content is less.     

Influence of Ti,B and Sr on the microstructure and mechanical properties of A356 alloy

In the present investigation, the microstructural and mechanical properties study of A356 alloy have been discussed. The microstructural aspect of cast A356 alloy employed in the present study is strongly dependent on the grain refinement (Ti and B) and modification (Sr). The mechanical properties such as PS, UTS, %E, %R, YM and VHN have been investigated. This paper deals with the combined effect of grain refinement and modification, which improves the overall mechanical properties of the alloy. It is also a well-known fact that the mechanical properties of cast A356 alloy were improved by subjecting suitable melt treatment such as grain refinement, modification and mould vibration, etc. The quality of castings and their properties can be achieved by refining of α-Al dendrites in A356 alloy by means of the addition of elements such as Ti and B which reduces the size of α-Al dendrites, which otherwise solidifies with coarse columnar α-Al dendritic structure. In addition, modification is normally adopted to achieve improved mechanical properties. Metallographic studies reveal that the structure changes from coarse columnar dendrites to fine equiaxed ones on the addition of grain refiner and further, plate like eutectic silicon to fine particles on addition of 0.20% of Al–10Sr modifier. The present result shows that a reduction in the size of α-Al dendrites, modification of eutectic Si and improvement in the mechanical properties were observed with the addition of grain refiner Al–3Ti, Al–3B and modifier Al–10Sr either individual addition or in combination. The change in the microstructure from coarse columnar α-Al dendrites to fine equiaxed dendrites and plate like eutectic silicon to rounded particles leads to improved mechanical properties.     

Microstructure and mechanical properties of high boron white cast iron with about 4 wt% chromium

The microstructure and mechanical properties of high boron white cast irons with about 4 wt% chromium before and after treating with rare earth magnesium alloy were studied in this article. The experimental results indicate that the cast irons comprise a dendritic matrix and interdendritic eutectic borides M₂B and M′_0.9Cr_1.1B_0.9 that distributed in the form of continuous network in as-cast condition. The matrix is made up of fine pearlite in the alloys with and without modification, but the grain size of the matrix is decreased greatly after modification. After water quenching at 1,303 K and tempering at 473 K, the matrix of the alloy mostly changes to lath-type martensite. For the alloy without modification the boride morphology remains almost unchanged after heat treatment. And a secondary precipitation of M₂₃(C,B)₆ compound appears in the central region of dentritic matrix grains. The morphology of the eutectic borides is changed to the form of isolated blocks after heat treatment and there is only little intragranular M₂₃(B,C)₆ particles in the matrix are found in the alloy modified with rare earth magnesium alloy. The modification by rare earth magnesium alloy can refine the primary austenite and the eutectic borides. Combined with a high austenitizing temperature the modification can improve the morphology of the borides which results in the improvement of toughness and tensile strength.     

Impact toughness of Al–Si–Cu–Mg–Fe cast alloys: Effects of minor additives and aging conditions

The effects of Sr modification and aging treatment on the impact toughness of a near eutectic Al–11%Si–2.7%Cu–0.3%Mg–0.45%Fe alloy were investigated. Charpy impact tests were performed on unnotched specimens in the as-cast and heat-treated conditions. It was found that the presence of Fe- and Cu-containing phases increases the alloy brittleness which reduces impact toughness. The eutectic Si phase also plays an important role, where the size/morphology of the Si particles controls the area of α-Al matrix available which affects ductility and toughness. Increasing the Mn content leads to an increase in the volume fraction of the α-Al₁₅(Mn,Fe)₃Si₂ phase formed and to sludge formation, which facilitates crack initiation and propagation. Crack propagation occurs mainly via the Al₂Cu and/or α-Al₁₅(Fe,Mn)₃Si₂ phases. In the non-modified alloys, the Si phase also plays a considerable role in the fracture process. The impact behaviour of aged alloys is influenced by the amount, size and morphology of hardening precipitates formed in the alloy, depending on the aging conditions. Aging at 240 °C produces a significant increase in the impact energy values of the low Mn-content alloys, as a result of alloy softening. The high Mn-content alloys also show a similar increase in impact energy values, but at a steady level across the same range of aging times, due to the persistence of the α-Al₁₅(Mn,Fe)₃Si₂ phase.     

Microstructural characterisation of nanoscale eutectics in melt spun Al-10 Sr alloy

Abstract

An Al-10 wt-%Sr alloy was cast using the melt spinning process to provide ribbons approximately 25 μm in thickness which could be used to investigate the effect of rapid solidification on microstructures. Nanoscale eutectic microstructures were found in the melt spun alloy. The microstructures consisted of two completely eutectic alternate bright and dark zones being in and out of contrast in the TEM. The eutectic Al₄Sr phases appeared stripelike and irregularly blocky in the dark zones, while regularly stripe-like in the bright zones. The typical size of the Al₄Sr phases was about 10 nm in thickness and 200 nm in length. The very fine eutectic microstructures resulted in the broadening of the XRD peaks of the melt spun Al- 10Sr alloy in contrast to the non-rapidly solidified alloy. Furthermore, the eutectic composition shifted from 2.4 wt-% in equilibrium to about 10 wt-% under rapid solidification processing conditions and eutectic temperature decreased from 654 to 647.1°C.     

Effects of solidification structure on tear resistance of Al–7% Si–0.4% Mg cast alloys

The tear resistance behaviour of Al–7% Si–0.4% Mg cast alloys was examined using Kahn‐type tear test specimens. Tests were performed for two permanent mould casts with an ordinary dendrite structure and a semi‐liquid die cast with a globular cell and fine grain structure. The microstructure of the two permanent mould casts was controlled by the cooling rates and the addition of Ti elements. Tear resistance was evaluated by the ‘pop‐in’ stress, the energies required for crack initiation, UE_i and the crack propagation, UE_p. Special attention was paid to an effective microstructural parameter for tear resistance improvement. Pop‐in, indicating sudden crack extension and arrest, was observed in all specimens. Homogeneous deformation occurs near the notch tip of the semi‐liquid die cast, characterized by a refined grain structure. Refinement of the grain size is more effective than that of the dendrite cell size or eutectic Si particle size to increase the energy for crack initiation. Unit propagation energy, UE_p, can be converted into a critical stress intensity factor, K_c, which in the semi‐liquid die cast was improved due to an increased amount of slant or shear fracture surface.