Casting generally uses vertical or horizontal water-cooled semi-continuous casting. In order to improve the microstructure and surface quality of the vertical casting, an electromagnetic crystallization tank, a short crystallization tank and a hot top casting method (see solidification of the metal) have also been developed. The water-cooled semi-continuous casting method introduces liquid metal into a water-cooled crystallizer through a launder, and cools the liquid metal to form a solidified outer shell, which is pulled by the casting machine base or uniformly lowered by its own weight to be separated from the crystallizer to form a billet. The process parameters vary greatly depending on the alloy composition and the size of the billet. Generally, the casting speed and cooling rate should be increased as much as possible to reduce the height of the crystallization tank. The casting temperature is usually 50 to 110 ° C higher than the liquidus of the alloy. In addition, a continuous casting and rolling process for aluminum strips has been developed.
Plate and strip production Flat roll rolling, the basic processes are hot rolling, cold rolling, heat treatment and finishing. Hard aluminum alloys such as LY12 and LC4 with complex chemical composition should be homogenized before hot rolling. The treatment temperature is generally lower than the eutectic temperature of the low melting point phase of the alloy by 10 to 15 ° C, and the temperature is maintained for 12 to 24 hours. The aluminum-clad aluminum alloy is placed on both sides of the billet by milling, and is welded by means of hot rolling. The thickness of the aluminum cladding layer is generally 4% of the thickness of the sheet. Hot rolling is generally carried out above the recrystallization temperature. Hot rolling can be carried out on a single-stand reversing mill or on multiple racks. In order to improve the yield and production efficiency, large ingot rolling is developed, and the ingot weight is more than 10 to 15 tons. For plants with an annual output of less than 100,000 tons, four-roll reversible hot rolling and hot coiling are generally used, and the thickness of the hot-rolled strip is about 6 to 8 mm. The factory with a production capacity of more than 100,000 tons will be hot-rolled in a single-stand or two-stand, three-stand and five-stand continuous rolling after the four-roll reversing hot rolling mill is opened. The strip thickness can reach 2.5-3.5. Millimeter. The hot rolled strip is rolled into a cold rolled billet. In order to ensure the best plasticity of the metal, hot rolling should be carried out in a single-phase state. The hot rolling blanking temperature of alloys such as LY11 and LY12 is 400 to 455 °C. The deformation rate of the first few passes is generally within 10%, and gradually increases thereafter. The deformation rate of pure aluminum and soft aluminum alloy can reach 50%, and that of hard aluminum alloy is about 40%. The total deformation rate of hot rolling can reach more than 90%.
Cold rolling is often carried out at room temperature. By cold rolling, thinner sheets and strips with precise dimensions, smooth surface and smoothness can be obtained, and work hardened sheets and strips with specific mechanical properties can be obtained. The cold rolling mainly adopts the belt type production process, and the cold rolling is carried out by using a four-roll reversible rolling mill or a four-roller irreversible rolling mill, and the current development of a non-reversible rolling mill for cold rolling. The rolling mill is equipped with hydraulic pressure reduction, hydraulic bending roll, thickness automatic control system or thickness automatic control system and shape control instrument. The micro-computer controls, records and stores various parameters to obtain accurate size and shape. Flat sheet metal, such as 0.18 mm strip tolerances up to ±5 microns. Small factories also have block methods for producing plates. The cold deformation rate of aluminum after annealing can reach more than 90%. The multi-phase hard aluminum alloy is cold work hardened and requires intermediate annealing. The cold deformation rate after the intermediate annealing is 60 to 70%. Hot rolling is lubricated with emulsion, which has been developed from emulsion to full oil lubrication. A multi-stage cooling system with separate nozzles is used to reduce friction between the aluminum sheet and the rolls, to cool the rolls, to control the roll type, to remove aluminum powder and other impurities, to obtain good surface quality and shape.
The coils after cold rolling and heat treatment are often finished on a roller straightener or on a continuous straightening machine. The plate after smoothing and quenching should be carried out during the aging period, usually within 30 to 40 minutes after quenching. The total calendering total deformation of the quenched plate should not exceed 2%.
Continuous casting and rolling of aluminum strips successfully tested in 1955 can produce thin sheets and aluminum foil blanks. China began to use this method to produce thin sheets in the early 1970s.