Typical application case of magnesium powder metallurgy in automotive lightweighting: performance comparison of gearbox housing and wheel hub

Automotive lightweighting reduces energy consumption and emissions through material innovation. Magnesium powder metallurgy, with its low density (1.74 g/cm ³), high specific strength, and near net forming ability, has shown the potential to replace traditional metals in key components such as gearbox housings and wheel hubs. Based on typical application scenarios, analyze its performance advantages and engineering challenges.

1、 Transmission case: a breakthrough in lightweighting from cast iron to magnesium powder metallurgy

Traditional material limitations:

The density of the cast iron shell is as high as 7.8 g/cm ³, accounting for 30% -40% of the total mass of the transmission assembly, and the thermal conductivity is poor (45 W/m · K), which can easily lead to an increase in oil temperature and affect transmission efficiency.

Although the aluminum alloy shell reduces the density to 2.7 g/cm ³, the die-casting process is difficult to meet the mechanical requirements of complex structures, especially in high load areas such as gear bearing seats where fatigue fracture is prone to occur.

Magnesium powder metallurgy solution:

Using powder metallurgy hot pressing sintering process, magnesium powder is mixed with alloy elements such as 8% aluminum and 0.5% zinc, and densified and formed at 400-450 ℃ and 80-120 MPa. The shell prepared by this process has significant advantages:

Lightweight effect: The weight is reduced by 60% -70% compared to cast iron. Taking medium-sized cars as an example, the magnesium alloy shell weighs only 12 kg (cast iron 35 kg), which helps the whole vehicle reduce weight by about 23 kg and fuel consumption by 3% -5%.

Performance improvement: The tensile strength reaches 220 MPa (surpassing cast iron's 180 MPa), the fatigue limit is 75 MPa (25% higher than aluminum alloy die-casting shell), and it can withstand the alternating load of gear meshing; The thermal conductivity is increased to 150 W/m · K (three times that of cast iron), and with the design of surface micro grooves, the oil temperature can be reduced by 10-15 ℃, extending the service life of lubricating oil.

Application example: A German car company has adopted Mg Al Zn magnesium powder metallurgy gearbox housing in high-end models, achieving dual optimization of lightweight and heat dissipation performance through material replacement.

2、 Wheel hub: Performance comparison between magnesium powder metallurgy and aluminum alloy

The core differences between magnesium powder metallurgy wheels and aluminum alloy wheels are reflected in density, mechanical properties, and process adaptability:

Lightweight advantage: Magnesium wheels have a density of 1.8-1.9 g/cm ³, which is 30% -40% lighter than aluminum alloy (2.6-2.7 g/cm ³). Taking 18 inch wheels as an example, magnesium products weigh only 7 kg (aluminum alloy casting 10 kg), and the decrease in unsprung mass significantly improves vehicle handling, with a 15% increase in steering response speed.

Mechanical performance balance: Through fine grain strengthening (grain size<10 μ m) and nanoscale second phase strengthening (such as Mg ₁₇ Al ₁₂ particles), the tensile strength of magnesium powder metallurgy wheels reaches 240-280 MPa, which is close to the forging level of aluminum alloys (300-350 MPa); Combined with surface rolling strengthening (introducing a 50-80 MPa compressive stress layer), the fatigue life can be increased from 500000 cycles to over 800000 cycles, meeting the service life requirements of passenger cars.

Cost and process: Magnesium powder metallurgy needs to solve the problems of powder oxidation prevention (inert gas sintering) and complex surface processing. The production cost is 30% -50% higher than that of aluminum alloy casting, but 20% -30% lower than that of forged aluminum alloy. It has a cost-effective advantage in the high-end market.

Application status: Although magnesium wheels still have bottlenecks in corrosion resistance (requiring graphene coating protection) and recycling systems, they have achieved breakthroughs in the fields of racing and high-end sports cars. For example, the Porsche 911 GT3 can be equipped with magnesium alloy wheels, balancing lightweight and handling performance.