Lightweight trend + low magnesium price + weight upgrade, magnesium alloy automotive parts enter fast lane. New energy vehicles have an urgent need for lightweight to extend their range. At present, magnesium alloy shells have entered high cost-effective range, possibility of magnesium alloy prices rising in short and medium term is small. At present, complex large structural powertrain shell has achieved an industrial breakthrough of 0-1, and is expected to start 1-N volume mode. Taking commonly used raw materials as an example, density ratio of aluminum alloy ADC12 and magnesium alloy AZ91D is 1.5, so under same volume, weight of aluminum alloy automotive parts is 1.5 times that of magnesium alloy. Compared with other lightweight materials, magnesium alloys also have advantages of anti-vibration and noise reduction, good die-casting performance, excellent cutting performance, rich resources and easy recycling.
New energy vehicles add three-electric systems, which increase weight of fuel vehicles by 5%-25%. Because battery energy density and safety are difficult to be compatible, extending battery life has always been a technical difficulty, and lightweighting can effectively improve battery life. According to "Key Technology Research on Lightweighting of New Energy Vehicles", a 20% reduction in weight of new energy vehicles will increase battery life by 5%-10%. Weight reduction of magnesium alloy shells can not only increase mileage, but also, at application level, because shell has underlying logic of homogenization and scalability, in the future, many companies will enter shell track like entering wheel hub. In order to effectively avoid internal circulation, in addition to price advantages, more attention should be paid to innovation and breakthroughs in technical routes.

 

Gearbox housing is a key component of gearbox. It assembles functional parts of reducer (such as shaft gears, parking, shifting and other related parts) into a whole and maintains correct position between them. Power is transmitted in a coordinated manner according to a certain transmission relationship. Appearance of housing needs to have artistic beauty, and arc ribs are mostly used. Under premise of ensuring overall stiffness and strength, design aesthetics is optimized.

 

Design principles:
1 Absorb force and torque during work;
2 Under various working conditions, ensure that shaft and gear have precise relative positions;
3 Ensure good heat transfer and heat radiation;
4 Isolate and attenuate noise; easy to assemble and disassemble;
5 Good rigidity and strength characteristics, light weight and reliability.

 

Material of automobile gearbox housing should have sufficient strength and good casting performance, and at the same time be low in cost. AZ91D alloy is selected, and alloy composition is as follows:

 

1. Die casting

2. Micro-arc oxidation surface treatment

 

1 Die-casting process
(1) Short filling time and fast speed
Due to physical properties of magnesium alloys and fact that its thermal conductivity is smallest among all die-casting alloys, fast filling is required. Generally, injection time of magnesium alloy is 30% to 35% shorter than that of aluminum alloy, and injection speed is 25% faster. Injection speed of upper and lower boxes is as high as 6 to 7 m/s, speed of extension box is also 5 to 6 m/s.
(2) Multiple runners and variable gate thickness
Also due to physical properties of magnesium alloys, in order to allow magnesium alloy liquid to fill cavity faster, it is required to have a larger inner gate area. However, this may lead to a decrease in inner gate filling speed, making far end of product not accessible. To achieve better filling. For this reason, design of runner adopts a combination of main runner and branch runner. Cross-sectional area of inner gate corresponding to each branch runner is smaller and its thickness is thicker. At the same time, cross-sectional area and thickness of inner gate vary according to different parts of product. Maximum thickness of inner gate is 3mm, and maximum cross-sectional area is 240mm2, which better guarantees quality of casting.
(3) Short pressure build-up time
Short pressure build-up time is basic requirement of all die-casting production processes, especially for magnesium alloy die-casting. Liquidus point of magnesium alloy is 596℃ and solidus point is 468℃. Under condition of temperature imbalance, the larger interval between liquidus and solidus points, the more inconsistent solidification time will be, making boost pressure ineffective in shrinkage compensation. Therefore, boost pressure of die-casting machine for producing magnesium alloys is required to be established at the moment after high-speed filling of cavity is completed and before solidification begins. Pressure build-up time of upper box, lower box, and extension box is within 30ms.
2 Die casting mold: Choose right mold
3 Sulfur hexafluoride gas protection

 

As a material used in new energy vehicles, magnesium has gained a firm foothold in automotive industry with its excellent performance. Main purpose of review is to use examples to illustrate wide application of magnesium alloys in automotive industry, and application of shells will increase confidence in developing new parts. At the same time, application of magnesium alloys still follows principle of using right materials in the right place, giving full play to its advantages such as light density and good fluidity, trying to avoid disadvantages such as low strength and easy corrosion. In the near future, new magnesium alloy structures and technologies will achieve greater breakthroughs to better meet growing demand for lightweight vehicles.