Aluminium Alloy Casting
Aluminium compounds are found naturally in most animals, minerals and vegetables and amounts to 8% of the earths crust. Aluminium ore, (Bauxite), is found mainly in Africa, West Indies, South America and Australia. There are also some deposits in Europe. Aluminium is the third most common crustal element, and the most common crustal metal on earth.
Pure aluminium is a soft lightweight material, but when mixed with quantities of other elements such as iron, silicon, zinc, copper, magnesium, tin, titanium, lithium, chromium, tungsten, manganese, nickel, zirconium and boron, a wide array of alloys can be produced each with its own physical and mechanical properties.
Aluminium alloys can be very strong and light (less than one third the specific weight of steel, copper or brass), ductile and malleable. Aluminium alloys are extremely conductive to both heat and electricity and aluminium when polished is the most reflective material known to man. Aluminium is unique in that it is 100 % recyclable and can be melted over and over again, it can be cast, rolled, extruded and fabricated into any shape or size. It has high resistance to corrosion.
Aluminium offers the user a wealth of valuable properties, which makes it the most common alloy used in the world today in fact more aluminium is produced than all other non-ferrous metals combined. Annual primary production in 1999 was about 24 million tonnes and secondary - recycled - production some 7 million tonnes. The total of 31 million tonnes compares with 14.1 million tonnes of copper, 6.0 million tonnes of lead and 0.2 million tonnes of tin.
Aluminium has an endless list of applications,
from its use as a packaging material for food to the construction
of spacecraft. Many of todays household items that we take for
granted are produced from aluminium.
Cast aluminium provided by W H Butler & Sons (Founders) Ltd.
W H Butler & Sons cast aluminium alloys both as sand castings and gravity die-castings. The main alloys being LM4, LM6, LM9 and LM25. If necessary any other alloy can, and would be used to meet individual requirements.
This alloy conforms to BS 1490. Castings may be in the as cast (M) or fully heat treated (TF) conditions. Suitable for most general engineering purposes where moderate mechanical properties are desirable. Its casting characteristics permit it to be used for the production of moderately thin forms and also for castings required to be pressure tight. In the heat-treated state it may be used for castings required to maintain a relatively high static loading.
Aluminium LM6 (High Silicon Alloy)
This alloy conforms to BS1490. LM6 exhibits excellent resistance to corrosion under both ordinary atmospheric and marine conditions. For the severest conditions this property can be enhanced by anodic treatment. The aluminium-silicon alloys possess exceptional casting characteristics, which enable them to be used to produce intricate castings of thick and thin sections. Fluidity and freedom from hot tearing increase with silicon content and are excellent throughout the range. The ductility of LM6 alloy enables castings to be easily rectified or modified in shape, e.g., simple components may be cast straight, and later bent to the required contour. LM6 is especially suited to castings that need to be welded although special care is needed when machining.
This alloy conforms to BS1490. Lm9 alloy is used where the fluidity and corrosion resistance of LM6 are required with high strength and hardness. It is equally suitable for both sand and die-casting. Very considerable tool wear occurs in machining this alloy, but there is not the same tendency to drag that occurs with high silicon alloys containing no other alloying elements, e.g. LM6.
This alloy conforms to BS1490. LM25 alloy is mainly used where good mechanical properties are required. The alloy is used where resistance to corrosion and particularly high strength is required. It is, in practice, the general-purpose high strength casting alloy. In its heat-treated form its tensile strength is increased from around 130-150 N/mm2 up to230-280 N/mm2.
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