Good article to share, detailed explanation of aluminum bronze smelting and characteristics
Aluminum bronze is a copper alloy with aluminum as the main alloy element. It is divided into binary aluminum bronze and multi-component aluminum bronze.
Alloys containing less than 7.4% aluminum have a single-phase a solid solution structure at all temperatures. Excellent plasticity and easy to process.
An alloy with an aluminum content of 7.4% to 9.4% exhibits a + β in the range of 1036 to 565°C; a two-phase structure. Under the cooling conditions of production, the β → a phase transformation process in the alloy is often not completed, and a part of the β solid solution is still retained. , and then eutectoid decomposition occurs into (a + γ2) eutectoid, where γ2 is a hard and brittle property. Its appearance will increase the hardness and strength and decrease the plasticity.
When an alloy containing 9.4% to 15.6% aluminum is slowly cooled to 565°C, β→a+Y2 transformation will occur, forming a eutectoid structure. The (a+γ2) structure in aluminum bronze is similar to the pearlite in annealed steel, with extremely obvious lamellar characteristics. However, the eutectoid decomposition of the β phase is relatively slow. When it is rapidly cooled, it will not have time to decompose, resulting in a metastable structure.
When aluminum bronze with an aluminum content of 8.5% to 11% is slowly cooled, the β phase decomposes into a eutectoid (a+2) and forms continuous, chain-like coarse γ2 particles, causing the alloy to become brittle. This phenomenon is called "Self-annealing" should be avoided in production.
The performance of aluminum bronze is related to the aluminum content. It has high mechanical properties, corrosion resistance, wear resistance, cold resistance, no sparks during impact, good fluidity, small segregation tendency, and dense ingots and castings can be obtained. Its disadvantage is that it easily forms columnar grains during solidification and is easy to
Easily contaminated by aluminum oxide film, difficult to weld, and not stable enough in superheated steam.
Adding alloy elements such as iron, nickel, manganese, etc. to binary aluminum bronze can further improve the performance of the alloy and expand its application scope.
Aluminum in aluminum bronze is a strong reducing agent. It is easily oxidized during the smelting process and generates A203 with a high melting point. If treated well, a continuous Al202 film will naturally form on the surface of the melt, which can prevent further oxidation of the melt. protective effect without any obligation
If it is not handled properly, suspended slag will be formed, which will be difficult to remove, thus becoming the source of slag inclusion defects in castings. From the perspective of improving the casting characteristics, structure and performance, phosphorus, arsenic, bismuth, zinc and lead are all elements with adverse effects and should be eliminated.
Iron and manganese are both high melting point elements. They should be divided into Cu-Fe (20%-30% Fe) and Cu-Mn (25%-35%
Mn), Cu-Al (50% AI), Cu-Fe-Al, Cu-Fe-Mn, Al-Fe and other intermediate alloys are added into the furnace to avoid a large amount of air intake and oxidation caused by long-term high-temperature melting. Burnout and energy waste.
When smelting aluminum bronze, 25% to 75% of this alloy process waste can usually be used. Chips containing oil, emulsion and moisture should be dried or remelted before being put into the furnace.
The melting point temperature of each alloying element in aluminum bronze from high to low is iron, manganese, nickel, copper, and aluminum. Due to the fusion of aluminum and copper
It is accompanied by a strong exothermic effect. This feature can be used to leave part of the copper material (commonly known as cooling material) in advance, and then add it to the furnace when aluminum is added in the later stage of smelting. In this way, the melt will not be overheated due to the exothermic effect associated with the addition of aluminum, and energy can be saved. Iron does not melt easily in copper, and manganese facilitates this process. Therefore, manganese should be added to the melt before iron. In order to avoid inclusions such as NiO and NiO.Cu2o in the melt, care should be taken to avoid oxidation of the melt. If necessary, deoxidation can be performed after the copper and nickel are melted.
Aluminum bronze is more suitable for smelting in medium and power frequency coreless induction furnaces. It is not suitable to be smelted in a power frequency cored induction furnace. The fundamental reason is that slag composed of A203 or A203 and other oxides easily adheres to the wall of the molten trench, causing the effective cross-section of the molten trench to continuously shrink until the entire cross-section of the molten trench is blocked by slag.
The melting atmosphere of the induction furnace is easy to control and the melting speed is fast, which is helpful to reduce or even avoid the risk of the melt absorbing a large amount of hydrogen and generating Al2O3 that is difficult to discharge from the melt. Although very fine Al2O3 may have the effect of refining crystallization, the greater danger is that Al2O3 may become the source of lamellar fracture defects in processed products.
Flux must be added for treatment. Flux has a relatively good wetting ability for A203 and can effectively clean slag and thus reduce the amount of slag.
In fact, when melting in medium- and power-frequency coreless induction furnaces, as long as the charge is good, it depends on the natural formation on the surface of the molten pool.
AL203 film can also prevent further oxidation and slagging of the melt.
When smelting aluminum bronze in a gas furnace, the melt is often blown with nitrogen or even hydrogen gas before pouring to remove the hydrogen absorbed by the melt during the smelting process. The amount of nitrogen blown depends on the quality of the melt. For example, the amount of nitrogen blown is 20L/100kg of melt. The melting temperature of aluminum bronze generally does not exceed 1200°C.
