Aluminum-titanium alloy profiles are widely used due to their low density, high specific strength, high temperature resistance and good oxidation resistance. However, the aluminum-titanium alloy profile has poor mechanical processing properties, which affects the wide use of the material.
Aluminum-titanium alloy profiles add alloying elements to industrially pure titanium to increase the strength of titanium. Titanium alloys can be divided into three types: a titanium alloy, b titanium alloy and a+b titanium alloy. The ab titanium alloy is composed of a phase of a and b. The alloy has stable structure, high temperature deformation property, toughness and plasticity, and can be quenched and aging treated to strengthen the alloy. The performance characteristics of titanium alloy are mainly manifested in:
1) High specific strength. The aluminum-titanium alloy profile has a low density (4.4kg/dm3), but its specific strength is greater than that of ultra-high-strength steel.
2) High heat strength. The aluminum-titanium alloy profile has good thermal stability, and its strength is about 10 times higher than that of the aluminum alloy at 300-500 °C.
3) Large chemical activity. Titanium can react strongly with oxygen, nitrogen, carbon monoxide, water vapor and other substances in the air to form TiC and TiN hardened layers on the surface.
Poor thermal conductivity. Titanium alloy has poor thermal conductivity. The thermal conductivity of titanium alloy TC4 at 200 ° C is 16.8 W / m · ° C, and the thermal conductivity is 0.036 cal / cm · sec · ° C.
Analysis of machining characteristics of aluminum-titanium alloy profiles
First, the titanium alloy has a low thermal conductivity of only 1/4 of steel, 1/13 of aluminum, and 1/25 of copper. Due to the slow heat dissipation in the cutting zone, it is not conducive to heat balance. During the cutting process, the heat dissipation and cooling effects are very poor, and it is easy to form high temperature in the cutting zone. After machining, the deformation of the parts is large, resulting in increased torque of the cutting tool and fast wear of the cutting edge. Reduced durability. Secondly, the thermal conductivity of the titanium alloy is low, so that the heat of cutting is not easily dissipated in a small area around the cutting blade, the frictional force of the rake face is increased, the chip removal is not easy, the cutting heat is not easily dissipated, and the tool wear is accelerated. Finally, the titanium alloy has high chemical activity, and it is easy to process with the tool material at high temperature to form a solution and spread, resulting in sticking, burning, and cutting.
Tool material selection should meet the following requirements:
· Sufficient hardness. The hardness of the tool must be much greater than the hardness of the aluminum-titanium alloy.
· Sufficient strength and toughness. Since the tool is subjected to a large amount of torque and cutting force when cutting the aluminum-titanium alloy, it must have sufficient strength and toughness.
· Sufficient wear resistance. Due to the good toughness of the titanium alloy and the sharpness of the cutting edge during machining, the tool material must have sufficient wear resistance to reduce work hardening. This is an important parameter for the selection of titanium alloy tools.
• Tool materials have a poor affinity with titanium alloys. Since the aluminum-titanium alloy has high chemical activity, it is necessary to avoid the formation and dissolution of the tool material and the aluminum-titanium alloy, resulting in sticking and burning.
Tests on common tool materials and foreign tool materials in China show that the effect of using high-cobalt tools is ideal. The main role of cobalt can enhance the secondary hardening effect, improve the hardness of red hardness and heat treatment, and have high toughness and wear resistance. Sexual, good heat dissipation, more suitable for processing aluminum-titanium alloy profiles.
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