Hypereutectic Aluminum-silicon Alloy Research Articles

Microstructural evolution in hyper-eutectic aluminium-silicon alloys with iron and nickel

Microstructural evolution in hyper-eutectic aluminium-silicon alloys with iron and nickel

Wear Behavior of CVD-Diamond Tools

Diamond cutting tools are often the only choice for the machining of high-strength and highly abrasive non-ferrous alloys. During machining, a complex interaction of different wear mechanisms takes place on the tools. This interaction considerably hinders a purposeful detection of specific wear mechanisms. Therefore, the objective is to systematically analyze the wear processes that occur when machining a hypereutectic aluminum silicon alloy with CVD-diamond tools. The main wear mechanisms are identified and the limits for the use of various CVD-diamond tools are indicated. The findings gained will serve in the further development of these high-performance cutting materials.

Improving the Wear Resistance of a Magnesium Alloy by Laser Melt Injection

The objective of this study is to improve the sliding wear resistance of the AZ91 E magnesium alloy, by means of dispersion of hard particles on its surface. Two kinds of powder and injection methods were applied. SiC powder, fed by Ar gas stream, was injected directly into a melt pool formed by laser beam. And the hypereutectic aluminum-silicon alloy was also injected in order to crystallize the fine Mg 2 Si intermetallic compound. These modified surfaces were evaluated by sliding wear test. SiC powder is dispersed uniformly at the surface of the AZ91E alloy, in proportion to the powder feeding rate. In the case of hypereutectic aluminum-silicon alloy, fine dendritic Mg 2 Si compound is crystallized uniformly. The matrixes of the modified layers changes from Mg solid solution to Al solid solution according to the powder feeding rate. And hardness of the layers are also changed. The wear depth of the SiC injected layer is almost zero, while that of the pin is increased by the sliding wear test. The modified layer using Al-30Si powder with the high powder feeding rate shows shallow wear depth and wear depth in the pin is also low.

Wear behavior of HFCVD-diamond coated carbide and ceramic tools

This paper describes the wear patterns on hot filament HFCVD-diamond coated carbide and ceramic tools during the cutting process, as well as the origins of these patterns. Knowledge of these phenomena is essential for a process-oriented application and for a full exhaustion of the tool's potential. A focal point is put on the processes turning, milling, and drilling. Fiber reinforced materials, a hypereutectic aluminum–silicon alloy, and a copper–aluminum alloy are used. Closest attention is paid to the abrasive and adhesive wear on the coated tools and similarly on the uncoated substrate carbide. The results show that CVD diamond coated carbide and ceramic tools enlarge the existing range of cutting materials. The wear protective diamond layer suggests an application of the tools in the high-speed range (HSC). Given the demands for an environmentally acceptable production, these tools can be applied in dry machining.

A Study on the Economics of Hypereutectic Aluminium-Silicon (Al-Si) Alloy Machining

Hypereutectic aluminium-silicon (Al-Si) alloys are used in auto-mobile components because of high wear resistance and good strength properties. In this study, the cutting of a hypereutectic Al-Si alloy with a single-crystal diamond tool for economical production was investigated by simulation. Tool life and the extraction rate of Si particles are inversely proportional to the depth of cut. By reducing the depth of cut, reductions of tool cost and tool changing time are achieved.

Surface Modification by Dispersion of Hard Particles on Magnesium Alloy with Laser

This study aims to modify the surface of magnesium alloy, AZ91E, to resist sliding wear by means of dispersion of hard particles on its surface. TiC and SiC powders, carried by inert gas stream, were injected into a melting pool formed by laser beam. And the powder of a hypereutectic aluminum-silicon alloy was also injected. These modified surfaces were evaluated to determine their resistance to sliding wear. The main results are summarized as follows: 1) Particles of TiC and SiC are dispersed in the cladding layer of AZ91E magnesium alloy. 2) In the case of hypereutectic aluminum-silicon alloy, fine particles of Mg 2 Si intermetallic compound are dispersed uniformly. 3) These modified surfaces result much higher resistance to sliding wear than the unmodified magnesium alloy. The cladding layers of TiC or SiC show high resistance, but opposing materials are worn. The Mg 2 Si dispersed cladding layer shows high resistance, however, the wear of the opposing material is little.

Aluminium precipitates in the primary silicon of as-sprayformed hypereutectic aluminium-silicon alloys

Precipitates have been observed in the primary silicon of as-spray-formed hypereutectic aluminium-silicon alloys with and without various alloy additions. The precipitates have been investigated using transmission electron microscopy and high-resolution transmission electron microscopy. They are aluminium based and generally adopt a spheroidal morphology, with diameters in the range of approximately 5-10nm, unless located on a stacking fault or grain boundary. Spray forming is a rapid solidification process and precipitation occurs because of the low solid solubility of aluminium in silicon (maximum of 0.016 +/- 0.003at.% at 1190 C). The morphology of the precipitates suggests that they form from aluminium or aluminium-rich liquid. The orientation relationships of several precipitates in one of the primary silicon grains have been determined.

Growth morphology of primary silicon in cast Al–Si alloys and the mechanism of concentric growth

Faceted growth of primary silicon crystals in cast hypereutectic aluminium–silicon alloys is studied by measurement of spacings between successive growth traces observed in microsections. A general equation, derived to specify conditions for stable growth of silicon crystal, is supported by spacing measurements. Some examples of departures from stable silicon growth are studied. Three stages in the development of faceted crystal growth are recognized, changing from spheroidal to faceted to unstable with increasing crystal diameter.

Role of the primary silicon particle on the dry sliding wear of hypereutectic aluminium-silicon alloy A390

The wear behavior of hypereutectic aluminium-silicon alloy A390 was investigated using a pin-on-disc wear machine under dry sliding conditions. The wear tests were performed within a load range of 10 to 300N at a constant sliding velocity of 0.5 m/sec. The microstructural and compositional changes that took place during wear were characterized by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analysis (EDXA) system. Based on the metallographic observations the role of the primary silicon particles was suggested. In a low pressure region, primary silicon particles supported the applied load and wear occurred mainly in the matrix. Thus the wear loss did not show much variation with the applied load. In the mid-load range, primary silicon particles did not yet fracture and thus supported the applied load in part. Transition from oxidative to metallic wear occurs mainly in the matrix and the increase of wear loss becomes sharper than that in a low pressure region. In the high pressure region, the fractures of primary silicon Particles occurred and wear loss increased sharply.

Properties and applications of forged hypereutectic aluminium-silicon alloys : G.Timmermans et al. (Catholic University, Leuven, Belgium.)

Solution treated aluminum 2024 alloy sheets were subjected to rolling at room and cryogenic temperatures. Aging time and mechanical properties were evaluated by microhardness measurements and tensile test, respectively. Microstructural parameters were assessed by applying modified Williamson–Hall and modified Warren–Averbach methods to the X-ray diffraction patterns. Interestingly, the mechanical behavior of the different as-rolled and post-roll aged samples was in correlation with the sub-grain sizes and dislocation densities. The sub-grain sizes of the as-rolled samples were smaller than 40 nm, and the dislocation densities were larger than 7.7×1015 m−2, which is related to the high strength of the as-rolled samples. After aging treatment, the ductility of the rolled samples increased significantly, this was justified by the decline in the dislocation density.

Hot forming of PM aluminium-silicon based alloys : S.Szczepanik. (University of Mining and Metallurgy, Crakow, Poland.)

Rapid Solidification Processing (RSP) offers significant advantages when applied to hypereutectic aluminium-silicon alloys: If compared to cast Al-Si alloys, higher strength levels, lower thermal expansion and increased wear resistance can be obtained. The materials studied are A119Si5Fe, A118Si5Fe2Ni, A117Si3.5Cu2Ni and A122Si3.5Cu2.5Ni (wt. %) made by the ‘Melt Spun Ribbons’-process and A125Si5Fe2Ni produced by spray-deposition.At this moment, these materials are applied in e.g. pistons for high performance engines. For economical use in mass-production, these materials have to be formed into their (semi-) final shape. This formability is subject of the paper. It gives an overview of this property for a variety of forming conditions, ranging from extrusion to sheet metal forming. The formability of the materials is quantified. A comparison with conventional materials is made and various formed parts are shown.

Scuffing Under Dry Sliding Conditions—Part I: Experimental Studies

The scuffing behavior of four materials sliding against 1018 carburiud steel is experimentally studied under dry sliding conditions. These materials are commercially pure aluminum (1100), die-cast hypereutectic aluminum-silicon alloy (390-T6), extruded Bi-containing eutectic aluminum-silicon alloy (DHT-3), and 1018 steel. The major emphasis is on the 390-T6 aluminum alloy. The environment for the tests is either air or tetrafluoroethane (R134a). The effects of load, sliding velocity, mechanical strength, environmental temperature, specimen size, time, loading history, and type of environment are evaluated. The mechanisms leading to scuffing are studied by examination of surfaces, subsurfaces and wear debris of specimens in the process of scuffing. Quantitative measurements of subsurface plastic deformation are also obtained. Based on the experimental observations it is concluded that scuffing is due to a subsurface material failure. This process involves initiation of cracks due to subsurface plastic deformation, propagation of these cracks leading to the removal of the existing protective surface layers and, finally, cold welding due to adhesion between bare metal surfaces. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

The fatigue response and fracture behavior of a spray atomized and deposited aluminum-silicon alloy

In this article the results of a recent study designed to improve our understanding of the cyclic fatigue and fracture characteristics of a spray atomized and deposited hypereutectic aluminum-silicon alloy are presented. Specimens of the alloy were cyclically deformed to failure at ambient temperature under fully reversed total strain amplitude controlled tension-compression loading. The alloy exhibited low cyclic plasticity and fatigue life under total strain amplitude controlled deformation. Cyclic stress amplitude controlled high-cycle fatigue characteristics were established at an elevated temperature (150 °C). The cyclic stress response, high-cycle fatigue life and fracture characteristics of the alloy are compared with a conventional ingot metallurgy processed counterpart and discussed in light of intrinsic microstructural features, nature and magnitude of stress, and ductility of the material.

Faceted growth of silicon crystals in Al-Si alloys

Primary silicon crystals in hypereutectic aluminum-silicon alloy castings frozen at moderate rates have been studied metallographically. Etched growth traces parallel to external facets were used to demonstrate that the majority of the crystals, though of widely varying external shape, grow in basically octahedral form, enclosed in {111} facets. Equations are developed that predict the limits within which true octahedral or spinel-type growth can occur. The equations are tested by measurements of growth trace spacings. Outside the predicted limits, there can be accelerated corner growth, which may result in hollow hopper crystals or even a dendritic form. Alternatively, a corner may be truncated by formation of a facet other than {111}.

Processing, microstructure and fracture behaviour of a spray atomized and deposited aluminium-silicon alloy

In this study a hypereutectic aluminium–silicon alloy was synthesized by spray atomization and deposition technique. Microstructure characterization studies were performed to provide an understanding of the influence of spray processing on microstructure of the hypereutectic alloy. Ambient and elevated temperature tensile tests reveal the spray-processed alloy to have better strength and ductility than a conventional ingot metallurgy processed alloy having the same chemical composition. The quasi-static fracture characteristics of the spray-processed alloy is presented and discussed in light of processing and intrinsic microstructural effects.

Wear of a spray-deposited hypereutectic aluminium-silicon alloy

This paper compares the wear characteristics of hypereutectic aluminium-silicon alloys processed using two different routes: the more recent spray-deposition technique and the conventional casting process. Unlubricated pin-on-disk wear tests revealed that the spray-deposited alloy has a better resistance to wear than its conventionally-cast counterpart. It is suggested that the increased hardness and the uniform distribution of the fine second phase in the spray-deposited alloy endowed it with a better wear resistance compared to the conventionally-cast alloy over the range of sliding conditions investigated presently.

Production of Hypereutectic Al-Si Alloys by P/M Route

In this work hypereutectic aluminium silicon alloys with high silicon content that are difficult to produce by casting, are produced by powder metallurgy (P/M) route. Different alloys are produced with varying silicon content. Aluminium silicon alloys are produced by both hot pressing and sintering of aluminium and silicon powder mixtures for the comparison. The production of hypereutectic Al-Si alloys by sintering of powder compacts is found to be unfeasible in terms of obtaining high density. The hardness and the density values of the alloys containing same amount of silicon, are higher in the alloy produced by hot pressing than the sintered alloys. The increase in hardness of the alloys is observed by increasing the silicon content. 100% theoretical density and 422 kg mm{sup -2} MHV hardness values are reached for the Al-67%Si composite which is hot pressed under 500 MPa and at 600 C. (orig.)

Semi-solid processing of novel MMCs based on hypereutectic aluminium-silicon alloys

This paper reports on the semi-solid processing (thixoforming) of spray-formed Al Si metal matrix composites (MMCs). In these novel MMCs, silicon—in quantities of up to 45 vol.%—was the reinforcing phase, rather than a ceramic. The project investigated all steps in the processing of the materials; mechanical tests on the products were carried out and demonstrator components were manufactured. It was shown that cylindrical billets of the MMCs could be formed in one step into intricate shapes at temperatures well below the liquidus. This confirmed that thixoforming is a safe, clean and practical method for the near net shape forming of components from materials that could be shaped only with difficulty by other techniques. The thixoformed MMCs exhibited very high specific stiffness, low thermal expansion, high specific strengths and high wear resistance.

Microstructural evolution in hypereutectic aluminium-silicon alloys during processing : G. Timmermans, L. Froyen (Katholic University, Leuven, Belgium)

Microstructural evolution in hypereutectic aluminium-silicon alloys during processing : G. Timmermans, L. Froyen (Katholic University, Leuven, Belgium)

Microstructural evolution in hypereutectic aluminium-silicon alloys during processing : G. Timmermans, L. Froyen (Katholieke Universiteit Leuven, Leuven. Belgium)

Microstructural evolution in hypereutectic aluminium-silicon alloys during processing : G. Timmermans, L. Froyen (Katholieke Universiteit Leuven, Leuven. Belgium)