The milling machine used in machining is very complex, and there are many kinds of milling cutters. “Milling” workpiece is: the workpiece is placed on the worktable and clamped with fixture, and the milling cutter is installed on the spindle. The spindle drives the cutter to rotate at high speed (main motion). The workpiece is driven by the worktable, which can realize the horizontal and vertical movement (feed motion). Under the joint action of the main motion and feed motion of the machine tool, the redundant part of the workpiece is removed. It can process plane, groove and curved surface on milling machine. The strengthening methods of aluminum alloy are as follows:
- Solution strengthening
The addition of alloy elements into pure aluminum forms aluminum based solid solution, which causes lattice distortion, hinders the movement of dislocations, and plays a role of solution strengthening, which can improve its strength. According to the general law of alloying, when forming infinite solid solution or high concentration solid solution alloy, not only high strength, but also excellent plasticity and good press workability can be obtained. Al Cu, Al Mg, Al Si, Al Zn, Al Mn binary alloys can generally form finite solid solutions and have high limit solubility (see table 9-2), so they have great solution strengthening effect.
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Another strengthening effect of alloying elements on aluminum is achieved by heat treatment. However, the transformation of aluminum during heat treatment is different from that of steel because there is no isomeric transformation of aluminum. The heat treatment strengthening of aluminum alloy is mainly due to the high solid solubility of alloy elements in the aluminum alloy, which decreases sharply with the decrease of temperature. Therefore, the supersaturated aluminum based solid solution can be obtained after the aluminum alloy is heated to a certain temperature and quenched. When the supersaturated aluminum based solid solution is placed at room temperature or heated to a certain temperature, its strength and hardness increase with time, but the plasticity and toughness decrease. This process is called aging. Aging at room temperature is called natural aging, and aging under heating conditions is called artificial aging. The phenomenon of increasing the strength and hardness of aluminum alloy during aging is called aging strengthening or aging hardening. The strengthening effect depends on the aging hardening phenomenon in the aging process.
- Excess phase strengthening
If the amount of alloying elements in aluminum exceeds the limit solubility, there will be a part of the second phase which can not be dissolved into the solid solution, which is called excess phase. In aluminum alloys, these excess phases are usually hard and brittle intermetallic compounds. They hinder dislocation movement in the alloy and strengthen the alloy, which is called excess phase strengthening. This method is often used to strengthen cast aluminum alloy and heat resistant aluminum alloy in production. The more the amount of excess phase and the more dispersed the distribution, the greater the strengthening effect. However, if there are too many excess phases, the strength and plasticity will be reduced. The more complex the structure of the excess phase and the higher the melting point, the better the thermal stability at high temperature.
- Refine the structure and strengthen it
Many aluminum alloys are composed of α solid solution and excess phase. If the microstructure of aluminum alloy can be refined, including refining α solid solution or refining excess phase, the alloy can be strengthened.
Because of the coarse structure of cast aluminum alloy, modification is often used to refine the alloy structure in actual production. Computer gong machining | mechanical parts processing | CNC machine tool processing | Dongguan high-speed computer gong machining modification is to add 2-3% modifier (commonly used sodium salt mixture: 2 / 3naf + 1 / 3nacl) to the molten aluminum alloy before pouring, so as to increase the crystal core and refine the microstructure. After modification, fine and uniform eutectic and primary α solid solution structure can be obtained, which can significantly improve the strength and plasticity of aluminum alloy.
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