Surface treatment method for processing titanium and titanium alloy forgings

At present, the global automobile industry has formed a "six big plus three small" competition pattern, namely, GM, Ford, Daimler-Chrysler, Toyota, Volkswagen, Renault-Nissan and other six major automobile groups with an annual output of more than 4 million vehicles. Plus three relatively independent car companies, namely Citroen-Peugeot (PSV), Honda, and BMW. At present, the key enterprises in China's automobile industry are FAW, SAIC, Dongfeng, Changan and BAIC. There are more than 5,400 enterprises nationwide. In 2005, more than 5.7 million vehicles were produced and sold.

At present, reducing fuel consumption and reducing hazardous waste (CO2, NOx, etc.) emissions have become one of the main driving forces and directions for technological progress in the automotive industry. Research shows that lightweight is an effective measure to save fuel and reduce pollution. For every 10% reduction in the quality of a car, fuel consumption can be reduced by 8%-10%, and exhaust emissions can be reduced by 10%. For this reason, countries all over the world are studying the issue of automobile lightweight. The preferred way to reduce the weight of automobiles is to replace traditional automobile materials (such as steel) with high-strength lightweight materials (aluminum, magnesium, titanium, etc.).

1. Advantages and disadvantages of titanium for automobiles

The application of titanium rods and titanium forgings in automobiles began in the 1950s, when the titanium industry was just born. Due to technical and price reasons, the application of titanium in automobiles has not attracted the attention of the industry. With the improvement of automobile energy saving and environmental protection standards, it has gradually become a hot topic of common concern in the international materials and automobile circles in recent years.

Titanium rods and titanium forgings have a variety of excellent properties and are the preferred materials for many different types of auto parts. The main advantages and applications are as follows.

(1) The low density is only 60% of the steel density, which can not only reduce the mass of the whole vehicle, but also reduce the inertia of motion for high-speed moving parts.

(2) High specific strength Among various metal materials, the specific strength of titanium is almost the highest, which can be used as load-bearing parts;

(3) The modulus of elasticity is small, only 50% of steel, and the fatigue strength is large, suitable for springs;

(4) Good heat resistance, can work for a long time at 200-650℃, suitable for high temperature parts;

(5) The coefficient of thermal expansion is small, which is 50% of that of stainless steel and aluminum, suitable for parts such as engine valves;

(6) Good corrosion resistance. The corrosion resistance is better than aluminum, magnesium and stainless steel. It can resist corrosion from the atmosphere, rain, moisture on antifreeze roads and high-temperature exhaust gas containing hydrogen sulfide. It is suitable for exhaust nozzles and other parts with harsh operating conditions. ；

(7) Good frost resistance. In the environment of minus 100℃, low temperature brittleness will not occur;

(8) Good formability. Parts of various shapes can be manufactured through stamping, hot forging, powder metallurgy, precision casting, etc.;

(9) Good decorativeness Through oxidation treatment, various decorative materials with bright colors can be formed.

In addition to TC4 titanium alloy rods and TC4 titanium forgings for automobiles, titanium materials such as TiAl-based intermetallic compounds, reinforced titanium rods, and titanium forgings have higher heat resistance, rigidity and wear resistance.

The advantages of using titanium in automobiles are: reduce quality and reduce fuel consumption; improve power transmission effects and reduce noise; reduce vibration and reduce component load; improve vehicle durability and protect the environment.

The disadvantages are: under normal circumstances, the wear resistance of titanium used in automobiles is not good, the elasticity is lower than steel, and it is difficult to machine. However, the wear resistance can be improved by coating or strengthening, and the elasticity can be improved by reinforcement. If the machining adopts near-net forming technology or other processing conditions, the shortcomings can be minimized. What really hinders the wide application of titanium rods and titanium forgings is the cost of titanium rods and titanium forgings, which are determined by the complexity of titanium's raw materials, smelting, and processing techniques. The smelting cost is basically the energy cost necessary to separate titanium from oxygen, and the processing cost is usually the processing and polishing cost. Polishing includes a process of removing the cracks or surface damage caused by a large amount of oxygen.
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