2017-05-15 11:20:34

Aluminum and Aluminum Alloys Casting Problems

Aluminum castings have played an integral role in the growth of the aluminum industry since its inception in the late 19th century. The first commercial aluminum products were castings, such as cooking utensils and decorative parts, which exploited the novelty and utility of the new metal. Those early applications rapidly expanded to address the requirements of a wide range of engineering specifications.

Alloy development and characterization of physical and mechanical characteristics provided the basis for new product development through the decades that followed. Casting processes were developed to extend the capabilities of foundries in new commercial and technical applications. The technology of molten metal processing, solidification, and property development has been advanced to assist the foundry man with the means of economical and reliable production of parts that consistently meet specified requirements.

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Aluminum Casting Alloy
we can do various kinds of aluminum sand casting, investment casting,carbon sand casting and stainless steel sand casting.

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Aluminum Sand Casting Mold
The sand casting parts used on vehicles, automobiles, arts and crafts, lamps, machines,etc.

Today, aluminum alloy castings are produced in hundreds of compositions by all commercial casting processes, including green sand, dry sand, composite mold, plaster mold, investment casting, permanent mold, counter-gravity tow-pressure casting, and pressure die casting.

Alloys can also be divided into two groups: those most suitable for gravity casting by any process and those used in pressure die casting. A finer distinction is made between alloys suitable for permanent mold application and those for other gravity processes.

Material constraints that formerly limited the design engineer’s alloy choice once a casting process had been selected are increasingly being blurred by advances in foundry technique. In the same way, process selection is also less restricted today. For example, many alloys thought to be unusable in permanent molds because of casting characteristics are in production by that process.

Melting and Metal Treatment
Aluminum and aluminum alloys can be melted in a variety of ways. Coreless and channel induction furnaces, crucible and open-hearth reverberatory furnaces fired by natural gas or fuel oil, and electric resistance and electric radiation furnaces are all in routine use. The nature of the furnace charge is as varied and important as the choice of furnace type for metal casting operations. The furnace charge may range from prealloyed ingot of high quality to charges made up exclusively from low-grade scrap.

Even under optimum melting and melt-holding conditions, molten aluminum is susceptible to three types of degradation:
* With time at temperature, adsorption of hydrogen results in increased dissolved hydrogen content up to an equilibrium value for the specific composition and temperature
* With time at temperature, oxidation of the melt occurs; in alloys containing magnesium, oxidation losses and the formation of complex oxides may not be self-limiting
* Transient elements characterized by low vapor pressure and high reactivity are reduced as a function of time at temperature; magnesium, sodium, calcium, and strontium, upon which mechanical properties directly or indirectly rely, are examples of elements that display transient characteristics.

Turbulence or agitation of the melt and increased holding temperature significantly increase the rate of hydrogen solution, oxidation, and transient element loss. The mechanical properties of aluminum alloys depend on casting soundness, which is strongly influenced by hydrogen porosity and entrained nonmetallic inclusions.

 
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