Magnesium alloy: "reducing the burden" for electric bicycles

"Magnesium alloy has a series of advantages. In the application of bicycles, it has high rigidity, high shock resistance and high bending resistance; it has good craftsmanship and is easy to be squeezed and deformed; the material can be completely recycled without waste, which is environmentally friendly. Clean, nothing harmful to the environment." At the recently held 3rd China Electric Bicycle Industry Development Summit, Russian professor Yurkin's views were widely recognized by people in the Chinese electric bicycle industry.

It is understood that magnesium and its alloys have the characteristics of low density, high specific stiffness and specific strength, good damping and easy recycling. They have been industrialized in the fields of aerospace, automobiles, motorcycles, and bicycles. The amount of magnesium used in bicycles has been used as one of the standards to measure the advanced nature of automobiles: European and American automobiles use 5.8-23.6 kg of magnesium alloy parts per car, and the amount of bicycles in my country is less than 10 kg. With the trend of lightweight and lightweight in recent years, China's electric bicycle industry has also begun to use magnesium alloys more and more.

Lightweight materials come to the fore

The person in charge of the Tianjin Bicycle Industry Association believes that the lighter and lighter electric bicycle products are the meaning of the development of energy-saving, emission-reduction, low-carbon products and green industries. From the perspective of the innovative requirements for improving the low-carbon quality of electric bicycle products for weight reduction and energy saving, the development and application of lightweight new engineering structural materials and high-performance batteries have revolutionary significance in improving the quality and performance of electric bicycle products and reducing the "carbon footprint". It is reported that the frame of the bicycle is the main load-bearing part of the bicycle and the most concentrated part of the overall weight. If you want to reduce the weight of the bicycle, you must choose materials that are lighter and have extremely high comprehensive mechanical properties. Magnesium alloy is one of the best choices.

Researchers from the School of Materials, Hebei University of Technology said that the mechanical properties of structural materials required to manufacture bicycle frames mainly include: density, elastic modulus, tensile length, tensile strength, fracture strength, and toughness. The tensile strength and hardness of magnesium alloys will also be improved accordingly after proper treatment. Appropriate methods can ensure that the magnesium alloy meets the requirements in terms of strength and elastic modulus, and a higher damping coefficient can ensure that the body absorbs part of the energy in the process of being impacted to reduce the impact on the rider, and at the same time, it can also improve the life of the bicycle. .

It is understood that due to the consideration of lightweight, many domestic electric bicycle companies began to carry out the application experiments of magnesium and aluminum alloys on bicycles a few years ago, and made major breakthroughs. At present, some electric bicycles on the market have begun to use lightweight metals such as magnesium alloys as the frame.

According to Professor Yurkin, Russia began to apply magnesium alloys earlier, not only in the field of bicycles. "From 1998 to the present, in addition to bicycles, we have also used magnesium alloy vehicles for disabled vehicles. At the Olympic Paralympic Games, Russian athletes used magnesium alloy vehicles and won many championships."

The production process faces huge challenges

Industry insiders believe that it is precisely because of the excellent weldability of magnesium alloys that the design of the frame can be arbitrary. But how to reduce production costs and establish large-scale production lines is the biggest challenge now.

It is reported that the magnesium alloy bicycle frame made by simple mold casting not only has poor performance, but also the cost of the mold is high. One model frame requires 3 to 9 different sized molds, and the price of one mold reaches $100,000, which is a higher cost. The common practice abroad is to obtain a hollow magnesium alloy tube through processing methods such as hot extrusion, and then complete the production of the frame by welding as required. This can not only ensure the quality requirements of the frame, but also save costs.

However, due to its own physical and chemical characteristics, magnesium alloys have great difficulties in welding, and satisfactory welding quality is not easy to obtain. The crystallization temperature zone of magnesium alloy is large, which is prone to hot cracks; the boiling point of magnesium is low, and after the temperature is further increased, its vapor pressure is 4 to 5 times higher than that of aluminum alloy at the same temperature, so once the welding temperature is too high, Magnesium will gasify, resulting in explosions and splashes; Magnesium has a high affinity for oxygen, and its oxide density is high, and it is easy to form inclusions; When magnesium is close to the melting temperature, it can strongly combine with nitrogen in the air to form brittle magnesium nitrides , which significantly reduces the mechanical properties of the joint; therefore, magnesium alloy welding is difficult, and defects such as cracks, pores, and splashes are prone to occur during welding, which significantly reduces the fatigue and other dynamic load performance of magnesium alloy welded joints. Application in vehicles presents challenges. It can be said that magnesium alloy welding technology is the main key technical problem to realize the large-scale application of magnesium alloy auto parts.

Researchers from the Advanced Joining Technology Laboratory of Dalian University of Technology revealed that through the "Tenth Five-Year Plan" and "Eleventh Five-Year Plan" technical research, my country has solved the connection problem of magnesium alloys. Dalian University of Technology has developed magnesium alloy bicycle welding structural parts, motorcycle welding structural parts and supporting magnesium alloy welding materials, and passed the bench test and road test, and met the export standard requirements. Among them, the magnesium alloy produced by welding technology Bicycles have been exported to EU countries with significant economic and social benefits.

The reporter learned from the Tianjin Bicycle Industry Association that the Tianjin Bicycle Industry Association has carried out the promotion and application of magnesium alloys, implemented the industrialization development plan of magnesium alloy bicycles, guided enterprises to increase investment and research and development efforts, and gradually mastered the development of magnesium alloy materials, welding and deformation. , anti-corrosion treatment and other process technologies, and gradually build a magnesium alloy material chain, parts supporting chain and talent technology chain with Tianjin Dongyi 10,000 tons of magnesium alloy materials and frame product development capabilities as the core, in order to achieve one million magnesium alloy bicycles And build a strong foundation for the industrialization development capabilities of electric bicycles.

The development of magnesium alloy electric bicycle products has also strongly promoted the promotion and application of lithium-ion power batteries. "In the process of lightweighting bicycles, the advantages of the two new products, the lightweight magnesium and lithium batteries, are outstanding, and they can be well combined on the bicycle to become a pair of golden combinations. They complement each other and rely on each other to become an electric The finishing touch and core competitiveness of bicycle weight reduction." said the person in charge of Baoding Dongqi Magnesium Alloy Profile Co., Ltd.