Aluminium alloys casting Problems

in Aluminium

Aluminium alloys casting has played significant role in development of aluminium industry since its inception in late 19th century. The first aluminium products were castings such as utensils and decorative parts which exploited the novelty and utilization of new discovery. Those early parts quickly expanded to meet the requirements of a wide range of engineering specifications.

Alloys development and analyzation of physical and mechanical features gave basis for product development through the decades which followed. Casting systems were processed to increase capabilities of foundries in new commercial and technical uses. The system of melted metal processing, solidification, and property development has been advanced to assist foundry man with means of cost effective and trustable production of components which regularly meet specific needs.

Nowadays aluminium alloy castings are manufactured in hundreds of ways by all commercial casting systems including green sand, dry sand, composite mould, plaster mould, investment casting permanent mould, gravity casting, low-pressure casting and pressure die casting.

Material constraints which previously limited the design engineers alloy choice once a casting process was selected are continuously being blurred by advancement in foundry techniques. Similarly process selection is also less restricted these days. Like the many alloys previously thought to be unusable in permanent moulds because of their casting features are in production by that very process.

Melting and metal treatment:

Aluminium alloys may be melted in various 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 furnace charge is as different and important as the choice of metal casting operations. The furnace charge may differ from pre-alloyed ingot of high quality to charge made up of low quality scrap. Even under best melting and melt holding situation melted aluminium is at risk to these types of degradation.

a) With time at temperature, adsorption of hydrogen results in increased hydrogen content.

b) With time at temperature, oxidation of melt occurs.

c) Transient elements featured by low vapor pressure and high reactivity are reduced.

Turbulence or agitation of melt and increased holding temperature, significantly increase the rate of hydrogen solution oxidation and transient element loss. The mechanical properties of aluminium alloys depend on casting soundness which is highly influenced by hydrogen porosity and entrapped non metallic inclusions. Aluminium alloys casting and products manufactured by them are things of the future due to their cost effectiveness and lightweight.

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This article was published on 2011/07/18