ALUMINIUM BRONZE alloys
Post 325 ⇒ by Gautam Shah →
Since more than 5,000 years the bronze and copper-based metals and their alloys have been used. At that point of time there was some realization that impurities and additives offer a range of properties. Specialized casting, treating and finishing techniques for different grades were improvised. The main reason for early discovery and use of copper was its natural occurrence in relatively pure form. Copper was too soft to make any tools. Tin is brittle and little rare in availability. First bronze was made out of copper and arsenic to form arsenic bronze. Later copper and tin were mixed to form bronze. Bronze was much harder and less brittle. Bronze alloys show little expansion on casting and setting allowing full filling up of the mould.
For centuries alloy metal scraps of copper, bronze, brass, tin, etc. of different mixes were reused, giving opportunity for learning the metallurgy. It was in 1800 that first combination of copper and aluminium was developed. It was rather a difficult process as the melting points of two metals are vastly different. It was then very expensive to produce. It was in 1900s that aluminium bronze billets were produced. Aluminium bronze is an alloy with aluminium as the main metal and copper is added to it. This is vastly different from normal bronze where main metal is copper and added with tin, or brass where main metal is copper and added with zinc. This began to change, when a variety of aluminium bronzes of differing proportions being developed. Other alloying agents such as iron, nickel, manganese, and silicon are also sometimes added to aluminium bronzes.
Aluminium bronzes are most valued for their higher strength and corrosion resistance as compared to other bronze alloys. Strong and corrosion-resistant alloys containing from 4 to 15 % aluminium are used for machine parts and tools. Aluminium bronze is used for jewellery and architectural hardware due to high tarnish resistance and golden colour. Their resistance to oxidation at high temperatures and to corrosion makes them suitable (acid) pickling equipment. It is non-sparking and non magnetic metal, and so used for brush holders, clamps for welding machines, hammers, mallets, wrenches and other tools for explosive prone atmospheres. Aluminium bronzes are weldable by brazing and metallic arc process Alloys with up to about 8 percent of aluminium can be cold-rolled into sheet for tube making.
Aluminium bronzes’ resistance to corrosion results from the aluminium component of the alloy, which forms a protective layer of aluminium oxide with atmospheric oxygen. Aluminium bronzes due to biostatic effect of the copper constituent, retards the colonization, by marine organisms including algae, lichens, barnacles, etc. on marine structures. Aluminium bronzes, are used for making coins.
Bronze and its alloys show little metal-on-metal friction. This property is used for making a cannon, covers on bullets, springs, bearings, bushings, automobile transmission pilot bearings, and similar fittings. Aluminium bronze sections are used for door and windows frames.