New process bonds Al/Mg inserts in aluminum castings.In recent years, there has been increasing pressure on the automotive industry The automotive industry is the industry involved in the design, development, manufacture, marketing, and sale of motor vehicles. In 2006, more than 69 million motor vehicles, including cars and commercial vehicles were produced worldwide. to improve quality, durability, cost, emissions and fuel economy. Demands have been made by legislators and environmental and consumer groups for lower emissions, improved vehicle safety and higher corporate average fuel economy (CAFE). To meet some of these demands, automakers have been working to reduce vehicle weight. One major aspect of weight reduction focuses on making lighter weight engines using aluminum alloy blocks to replace traditional cast iron blocks. However, most of these aluminum engine blocks still use cast iron liners in the bores. The iron insert is immersed in a bath of molten aluminum and placed in the mold, where the aluminum engine block is cast around it. Unfortunately, the use of iron adds significant weight to the engine. Also, cast iron does not conduct heat away from the cylinder as well as aluminum would. Without good conductivity and heat dissipation Noun 1. heat dissipation - dissipation of heat chilling, cooling, temperature reduction - the process of becoming cooler; a falling temperature , the cylinder's temperature rises, imposing higher temperature-related stresses and wear on the engine's internal components. A better alternative to iron inserts is to use cast-in-place aluminum alloy or composite cylinder liners, employing permanent mold or squeeze-cast aluminum alloys for the block. The result is further weight reduction, better heat dissipation, better wear and scuffing resistance and reduced cost. All the above benefits can be realized if there is a high-integrity metallurgical bond between the liner and the aluminum alloy block. One problem with using an aluminum insert is that aluminum reacts instantly with oxygen to form a 40-50 A (Angstrom angstrom (ăng`strəm), abbr. Å, unit of length equal to 10−10 meter (0.0000000001 meter); it is used to measure the wavelengths of visible light and of other forms of electromagnetic radiation, such as ultraviolet ) thick oxide film on its surface, and the thickness of the oxide film increases as temperature increases. This oxide film acts as an insulator insulator Substance that blocks or retards the flow of electric current or heat. An insulator is a poor conductor because it has a high resistance to such flow. Electrical insulators are commonly used to hold conductors in place, separating them from one another and from , preventing the wetting of the molten alloy with the insert material. Therefore, it is not possible to obtain a metallurgical bond between the insert and the casting alloy, leaving a major weak point in a component. The Metabond process has been developed to solve this problem. With this method, the insert--which can be aluminum, magnesium or composites designed to provide special properties in a localized area--is dipped in a bath of molten zinc-base alloy that contains about 0.1-0.5% magnesium and 2-10% aluminum by weight. The effect is to coat the insert with the zinc-base alloy. Magnesium in the bath forms magnesium oxide magnesium oxide: see magnesia. (MgO) and spinel spinel, magnesium aluminum oxide, MgAl2O4, a mineral crystallizing in the isometric system, usually as octahedrons. It occurs as an accessory mineral in basic igneous rocks, in aluminum-rich metamorphic rocks, and in contact-metamorphosed (Mg[Al.sub.2][O.sub.4]), which will crack and weaken the aluminum and zinc oxide zinc oxide, chemical compound, ZnO, that is nearly insoluble in water but soluble in acids or alkalies. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. layers and enable the casting material to more easily wet the insert's surface. Besides coating the insert, dipping it in the molten bath for at least three minutes "Three Minutes" is the 46th episode of Lost. It is the twenty-second episode of the second season. The episode was directed by Stephen Williams, and written by Edward Kitsis and Adam Horowitz. It first aired on May 17, 2006 on ABC. raises its temperature to above the liquidus temperature The Liquidus Temperature, TL or Tliq, is mostly used for glasses and alloys. It specifies the maximum temperature at which crystals can co-exist with the melt in thermodynamic equilibrium. Above the Liquidus Temperature the material is homogeneous. of the zinc-base bath (about 728F--still significantly lowerthan the aluminum liquidus temperature). In this way, the insert is sufficiently preheated to reduce the temperature gradient temperature gradient n. The rate of change of temperature with displacement in a given direction from a given reference point. temperature gradient between the insert and the molten casting material, minimizing contraction stresses and shrinkage after the casting has solidified. After immersion in the bath, the coated insert is immediately placed in the mold and the casting poured around it. Using a preheated mold, the insert holds its temperature well, and a cycle time of one minute before pouring the casting is generally sufficient. Once the casting is poured, the residual zinc-base alloy layer fuses to both the insert and the casting, forming a strong metallurgical bond. Other than a holding furnace for the molten bath, the process requires no special equipment. It is particularly suitable as a low-cost, mass-production approach for producing aluminum composite liners in aluminum engine blocks, piston ring groove reinforcement and dual-alloy aluminum castings. Foundries can also cast many other components that require aluminum inserts. Advantages of the method include: * it can be used in a conventional foundry setup; * it is suitable for mass production; * it does not require special operator skills; * it does not involve toxic materials; * it is a cost-effective and better method to integrate aluminum-or magnesium-base metal matrix composites Metal matrix composite A material in which a continuous metallic phase (the matrix) is combined with another phase (the reinforcement) that constitutes a few percent to around 50% of the material's total volume. in a casting than the infiltration of proform pro·form or pro-form n. An item in a sentence, typically a pronoun, verb, or adverb, that substitutes for a constituent phrase or clause, as the words he and so in the sentence He said so, with the pronoun he fibers. The applications of the patented process are not just confined to aluminum inserts. It is equally adaptable to magnesium-base materials, such as wrought magnesium alloys, castable magnesium alloys, and magnesium-base metal matrix composites. |
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