L7 is the first mass-produced product of Zhiji Auto. Medium and large pure electric sedan Zhiji L7 has been officially launched for more than a year. Its power part is equipped with a front and rear dual-motor four-wheel drive system with a total power of 425KW, a peak torque of 725Nm, a CLTC range of 615Km, and an acceleration time of 0-100Km/h of 3.87 seconds. Rear axle main drive motor is a customized black label version of a high-power magnesium alloy direct waterfall oil-cooled motor.
Magnesium alloy shell product of complete electric drive system of Zhiji L7 weighs 14.2Kg, which is more than 7Kg lighter than traditional aluminum alloy materials, and has a significant effect in weight reduction. Magnesium alloy shell product of complete electric drive system of Zhiji L7 is the first mass production application of magnesium alloy materials on new energy electric drive shells. It is understood that many magnesium alloy new energy electric drive assembly products developed by SAIC have been successfully mass-produced.
According to Zhang Ji, deputy general manager of Xingyuan Zhuomei, Zhiji L7 model is currently one of the largest magnesium alloy parts and components in mass production in automotive field at home and abroad, has taken lead in realizing new application scenarios for magnesium alloys. Xingyuan Zhuomei has a complete production closed-loop system, has both production and manufacturing capabilities in die-casting-burr-passivation-cleaning-finishing and other process flows, so it has a strong competitive advantage in application of magnesium alloy new energy vehicle upper shells.

Lightweight trend + low magnesium price + weight upgrade, magnesium alloy automotive parts enter fast lane New energy vehicles have an urgent need for lightweighting to extend their range. Current magnesium alloy shell has 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 automobile parts is 1.5 times that of magnesium alloy. Compared with other lightweight materials, magnesium alloy also has advantages of anti-vibration and noise reduction, good die-casting performance, excellent cutting performance, abundant resources and easy recycling.
New energy vehicles add three-electric systems, which increase weight of fuel vehicles by 5%-25%. Because energy density and safety of batteries 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 shell can not only improve driving range, but also, in 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 breakthrough of technical routes.

 

Gearbox shell part is a key component on gearbox. It assembles functional parts of reducer (such as shaft gears, parking, shifting and other related parts) into a whole, and keeps correct position between each other. 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:
01 Absorb force and torque during work;
02 Under various working conditions, ensure that shaft and gear have precise relative positions;
03 Ensure good heat transfer and heat radiation;
04 Isolate and attenuate noise; easy to assemble and disassemble;
05 Good rigidity, 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
Die casting machine debugging Die casting mold installation
Mold preheating, coating, mold closing (mold closing)
Pouring and injection, pressure holding
Mold opening, core pulling and part removal Surface quality inspection
Cleaning (renovation)

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 the 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, and 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, so that far end of product cannot be filled well. For this reason, design of runner adopts a combination of main runner and branch runner. Cross-sectional area of gate corresponding to each branch runner is smaller and its thickness is thicker. At the same time, cross-sectional area and thickness of gate vary according to different parts of product. Maximum thickness of 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 a basic requirement for 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 building 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 illustrate wide application of magnesium alloys in automotive industry with examples, and application of shells will increase confidence in development of new parts. At the same time, application of magnesium alloys still follows principle of using right materials in right places, 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, greater breakthroughs in new magnesium alloy structures and technologies will better meet growing demand for lightweight vehicles.