Military aluminum alloy
The 6151 alloy was born in the United States in the mid-1930s. Its prototype alloy was listed as a very alloy by the American Aluminum Association on December 12, 1963. There are currently five alloys commonly used: 6151. 6351, 6351A, 6451, 6951 alloy. Except for the 6351A, which is a French alloy, the others are all American alloys. These alloys are widely used in military weapons for the manufacture of crankcase forgings and rolling rings, mines and machine forgings. Any part that requires good forging properties, high strength and good corrosion resistance can be processed with this alloy. Before 1954, it was called 51S in the United States and was ordered to be 6151 alloy in 1954.

chemical composition

The chemical composition of the 6151 alloy is shown in Table 1. In terms of composition, the 6951 alloy has the lowest Si content, which is only about 35% of other alloys. Therefore, its strength property should be the lowest, but it contains 0.15% Cu - 0.40% Cu. While other alloys do not contain Cu, their mechanical properties are almost indistinguishable.

Mechanical properties

The lowest mechanical properties of Alloy 6151 are shown in Table 2. The gauge length of the sample is 50 mm or 4 d (d is the diameter of the sample). The 6151 alloy has no low-temperature brittleness and can be used to process parts working at extremely low temperatures. The tensile strength Rm=330N/mm2 at 25°C, the yield strength Rp0.2=298N/mm2, and the elongation A=17%. When the temperature dropped to 200 °C, the performance increased in all directions, reaching 395 N/mm2, 345 N/mm2, and 20%, respectively. The working temperature of the 6151 alloy should not exceed 120 °C.

Physical properties

The density of 6151 alloy at 2 °C is 2700kg/m3; the liquidus temperature is 649°C, the solidus temperature is 588°C, and the average linear expansion coefficient of -50°C-20°C is 21.8μm/(m·k), 20°C— - 100 ° C average linear expansion coefficient 23.0 μm / (m · k), 20 ° C - 200 ° C average linear expansion coefficient 24.1 μm / (m · k), 20 ° C - 300 ° C average linear expansion coefficient 25.0 μm /(m·k).

Equivalent volume conductivity of 6151 alloy at 20 °C: 54% IACS for O-state material, 42% IACS for T4 state, 45% IACS for T6 state; Resistivity at 20 °C: 32nΩ·m for O-state material, T4 41nΩ·m in the state, 38nΩ·m in the T6 state; specific heat capacity 895J/(kg·K) at 20°C; thermal conductivity at 20°C: 205W/(m·k) of the O-state material, 163W/ in the T4 state (m·k); 175 W/(m·k) of the T6 state.

The 6154 type alloy has a potential of -0.83 V for a 0.1 N calomel electrode in a solution containing 53 g of NaCl/L + 3 g of H 2 O 2 /L at 25 ° C.

Process characteristics

The annealing specification of the 6151 alloy is 413 ° C / (2 h - 3 h), and the furnace is cooled to 260 ° C at a cooling rate of not more than 27 ° C / h, and then air-cooled. Solution treatment temperature (510 ° C - 525 ° C) / 4 min, quenching in room temperature water, large forgings quenched in water at 65 ° C - 100 ° C. Artificial aging specification (165 ° C - 175 ° C) / (8h - 12h). The hot working temperature is 260 ° C - 480 ° C.

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