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Hypereutectic Al-25%Si Alloy Alternative AluSil Cylinder Liner
In the ALUSIL process ,the entire engine housing consists of a hypereutectic aluminum silicon alloy. The increased silicon content, which contains 17% silicon in the most frequently used ALUSIL alloy, is typical of such a hypereutectic alloy.Currently available and mature products in our company,e.g Al-25%Si alloy(AlSi25Cu4Mg) cylinder liners can instead of the casting AlSi17Cu4Mg alloy. The hypereutectic Al-Si alloys material are fabricated by our proprietary technology of Rapid Solidification at T6 condition(Solution heat treatment process)..Herein,the silicon content by the weight of 20%~35% in the alloy which features excellent wear-resistance,high temperature strength,heat stability as well as high abrasion resistance.The AlSi25 alloys are relatively easy to honing and grinding,both for bars billets and cylinder sleeves tubes.They are machinable to a very fine finish(0.5μm~5μm) with carbide or poly-crystalline diamond(PCD) tools.Due to these cylinder liners are produced by extrusion of billets,so the cost is higher than that of cast iron ones.The Al-25%Si alloy cylinder liner makes us an anttractive(and possible) only for top level cars.
Competitive advantages of using the Al-25Si alloys in engine components:
●A lightweight cylinder block can be achieved.
●In comparision of cast iron cylinder liner,the thermal conductivity and coefficient of thermal expansion is far higher and greater than that of cast iron ones,a good tight contact between the cylinder liner and cylinder block body can be achieved upon temperature elevation and, thus, an internal-combustion engine having a good heat-dissipation characteristic can be provided.
●In the condition of ultra-mild wear(UMW),the microstructure(SEM) shows the silicon particles of Al-25%Si alloy is effective maintaining a minimal surface damage,thus,improve the wear-resistance.
●As we mentioned earlier, the inner-wall temperature of Al-25Si alloy cylinder liner can be kept low and the life of the lubricating oil can be prolonged.
●By using the hypereutectic Al-25%Si alloy cylinder liners,thanks to the friction coefficient is low, the friction loss which occurs between the piston rings and the cylinder liner can be lessened and, thus, the mileage can be improved.
Hypereutectic Si-Al alloys are typically defined as those where the silicon content is equal or more than 17 wt %.As a versatile material,the hypereutectic Al-Si alloys have been commonly used in automobiles,motorcycles and tactical vehicles.Applications of the Al-Si alloys in the automotive industry,including engine blocks and parts of engines,particularly,cylinder liners.The following reason is why we introduce the aluminum alloys cylinder liner for the engine blocks. As we all known,fuel consumption is a serious problem exsiting in the operation of automobiles.More fuel consumption also means greater pollution emissions.The reduction in cylinder distortion (higher dimensional stability) that is possible with this alloy results in less noise and friction; engine-oil consumption and exhaust emissions are thus reduced, e.g 1kg hypereutectic Al-Si alloy can replacement 3kg casting alloy,the overall performance of automobiles can be enhanced.The hypereutectic Al-Si alloys material shows good wear-resistance combined with low coefficient of thermal expansion and have a high strength-weight-ratio.Hereby,it can remarkably improved the workability and ductility for the highest operation demands.Finally, the blanks are specially treated in an environmentally friendly process, aqueous exposure. The resulting smooth surface structure improves friction characteristics and cuts the engine's oil consumption and hydrocarbon-emissions levels.Thereby，curretly the use of cyliner liners made of hypereutectic aluminum alloys have been preferred and applied by many automobile manufacturers.
Property Characteristics of Hypereutectic Al-Si alloy
Low coefficient of thermal expansion;lower weight;dimensional stability;higher thermal conductivity;Excellent wear-resistance and corrosion resistance.The hypereutectic Al-Si alloy possess these combination performances which extremely suitable for manufacturing lightweight and wear-resistance parts.
The properties of hypereutectic Al-Si alloy,encompassing the casting performance,mechanical property,abrasion property and cutting machining.
A large amount of latent heat is released when the primary silicon precipitate out,the commonly used eutectic al-si alloy has better fluidity than eutectic alloy.However, liquidity will begin to decline after the Si content exceeds 18%. As the silicon content in the alloy increases, the linear shrinkage decreases.While with the expansion of the crystallization temperature range, some casting defects will gradually appear, such as alloy shrinkage tendency increases, reduced air tightness, that is, casting performance.
The alloys can obtain the satified mechanical properties if through the matchable modification.As the temperature increases,the alloy strength reduction but improve the ductility. Under the condition of select suitable composition and modification treatment,the high temperature strength of hypereutectic Al-Si alloy is superior than that of eutectic alloy.
As the increase of silicon content,the primary silicon volume percentage will increase in the alloy,so that improve the abrasion resistance of the alloy.
Comparation to the cocrystallizing type and eutectic alloy, the wear rate of hypereutectic of Al-Si alloy is 0.3~0.5 times than hypoeutectic alloy,is 0.1~0.2 times than that of eutectic alloy.In general,the hypereutectic Al-Si alloy has excellent wear-resistance.
Owing to the tool is worn very easily and roughness surface.The solution to this problem is to use the diamond tools,or add a little lead(Pb) or bismuth(Bi) in the alloy composition.
High Temperature Strength and Dimensional Stability
The current research focuses on the hypereutectic alloys with silicon content below 30%. Due to its high thermal conductivity and controllable thermal expansion coefficient, high-silicon aluminum alloys are used in electronic packaging materials,e.g 27Si-73Al to 70Al-30Al controlled expansion alloy.
Currently,Erbslöh Aluminium GmbH has fabricated range of hypereutectic Al-Si alloy products and successfully entered into mass-production stage,e.g.crankcase.measurement technology,oil pump gears,connecting rods and bearing caps etc.In Japan,more and more manufacturers prefer to select the hypereutectic Al-Si alloy as the raw material of pistons,and expand the application to the truck and commercial vehicles.
Though the hypereutectic Al-Si alloy is still in the state of rearch and development in China,Tianjin Baienwei New Material Technology Co.,Ltd as an individual large scale company which has produced series of aluminum alloy products,e.g.advanced piston and cyliner sleeves has reached the world level standard.The products manufactured has recognized by our clients in the Germany and North America.Baienwei Co.Ltd stick to the principle of ‘’Technological innovation and rejuvenate the state by industrialization’’.We serve our markets with both standard products and customized driven products and milling CNC machining service.Through years of great effort,significant progress has been made in the development of automotive assembly parts.