Introduction to aluminium bronze smelting

Introduction to aluminium bronze smelting
Aluminum is the most important alloying element of aluminum bronze. According to elements are added or not, aluminum bronze is divided into simple aluminum bronze, namely binary Cu-Al alloy and complex aluminum bronze, namely multiple copper alloy based on copper and aluminum with elements such as Fe, Ni, Mn and Zn... Aluminum bronze has good casting properties. When the aluminum content is less than 7.4% (without special instructions, refers to the mass fraction), all aluminum bronze alloys in the solid state are a single alpha; Phase solid solution, good alloy plasticity, good processing formability. When the aluminum content ranged from 7.4% to 9.4%, the tissues were + at 1036℃ to 565℃.Bimodal structure, but due to the impossibility of an ideal slow cooling rate during the casting process,; It doesn't completely convert to alpha; Residual; As the temperature decreases, eutectoid transition occurs, i.e. beta.& rarr;α+γ2,γ2 is a solid solution based on Cu9Al4, which is a hard brittle phase with body centered cubic lattice. Its precipitation will reduce the plasticity of the alloy, but increase the strength and hardness of the alloy. In addition, due to its relationship with the & Alpha alloy; The great difference in the composition of the phase structure will cause the formation of electric couple due to the difference in potential in the corrosive medium, so it will seriously affect the corrosion performance of aluminum bronze.The aluminum bronze alloy with the aluminum content between 9.4% and 15.6% occurred beta when cooling slowly from high temperature to 565℃.→α+γ2. The tissue is lamellar. The subeutectoid aluminum bronze with the aluminum content between 9.4% and 11.8% is beta during the rapid cooling process. Nondiffusion phase transition occurs and spicules and beta are formed.&l squo; Phase and martensite tissue. The order of tissue change of pereutectoid aluminum bronze with aluminum content greater than 11.8% was the initial &beta. Phase solid solution turns into beta.1. The ordered solid solution then changes into & Beta with the increase of aluminum content in the alloy;’ Martensite, β& lsquo;+γ’ Mixture or acicular β& lsquo; Martensite. When the aluminum content is greater than 9.4%, the microstructure of aluminum bronze alloy after quenching is mainly & Beta.& rsquo; Martensite. Because & beta;& lsquo; The hardness and strength of phase are higher than & Alpha. Therefore, it can be used in the manufacture of components that require wear resistance of aluminum bronze. In addition, & beta;’ Phase is a kind of metastable tissue, and different tissues can be obtained by tempering it at different temperatures. Hypereutectoid aluminum bronze with aluminum content greater than 11.8% is a typical solid solution strengthening alloy, which is often strengthened by heat treatment in actual production. Aluminum bronze can be strengthened by heat treatment. The principle of strengthening is to obtain the mesostable structure of martensite by quenching, so as to strengthen the alloy.
The excellent properties of aluminum-bronze were discovered as early as 1910, but at that time the casting technology was not very developed, such as easy absorption of hydrogen in smelting, large involvement of oxide in pouring, and so on, which delayed its practical application. In addition, the above problems also exist in the metallographic structure, that is, high strength aluminum bronze should be made by α+β Composition, but due to & Beta; Phase cooling will lead to beta;& rarr;α+γ The eutectoid transformation and embrittlement of 2 deteriorates the mechanical properties and corrosion resistance.Although this transformation is prevented at high cooling rates, it is unavoidable for large propellers (with slow cooling rates), so composition adjustment must be used to prevent this transformation. There are two ways in practical application: first, add a large amount of manganese, delay & Beta; Phase eutectoid transformation, thus, stable & Alpha can be obtained at room temperature;+β The tissue, this is high manganese aluminum bronze;2. Add a lot of nickel to make α/α+β The dissolution limit of the phase moves towards the aluminum side to avoid beta. Phase exists, thus in α A small dispersed K phase is formed within the phase, which is high strength nickel-aluminum bronze.
Excerpt from National Material environment Corrosion Platform
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