More than 600 aluminum parts are used in body, chassis, power and transmission systems. Amount of aluminum used in automobiles in various countries/regions has shown rapid growth, with North America and China being the most significant. Aluminum is mainly used for body structural parts, wheels, body panels, transmission systems, cylinder blocks and heads; amount of aluminum used in C-class and above cars is much more than in A and B-class cars.
Comparison of types of aluminum used in China and foreign automobiles: Aluminum for castings accounts for more than 60%, and proportion of aluminum plates used increases year by year, especially for C-class and above models.
Proportion of aluminum-on-aluminum castings used in China automobiles is higher than that in Europe and United States. In 2018, 3.8 million tons of aluminum were used in automobiles (2.9 million tons of castings). 2030: 9.1 million tons. Development of new energy vehicles has promoted increase in aluminum consumption, has significantly increased proportion of sheets and extruded materials.

 

 

Some researchers pointed out that aluminumization of chassis parts has obvious lightweighting effect and significantly improves vehicle performance. Auminization rate abroad is relatively high, but China it is much lower than abroad. It is mainly used in high-end self-branded cars and pure electric cars, but penetration rate is only about 10%. Steering knuckle products have the highest penetration rate among chassis parts, and the most technically difficult part is subframe. Product yield is low, dimensional accuracy needs to be improved, welding joint performance and welding deformation control level are low.
Structural parts attach great importance to lightweight efficiency. Design of lighter parts structures, development of higher-performance materials, higher production efficiency and yield rates are main trends in the future.

Problems with traditional melting and casting process of A356.2+: (1) Yield strength cannot meet design requirements, and elongation cannot be stable ≥ 9% (2) Eutectic silicon has a low degree of deterioration and is prone to thick needles and flakes, which seriously affects mechanical properties, especially elongation. (3) α-Al is not refined and has obvious dendrites, which affects strength and elongation. (4) Eutectic silicon in structure after heat treatment is worm-shaped, and spheroidization effect is not good, which affects strength and elongation of alloy.

 

Function and performance requirements of steering knuckle
Main structure and force-bearing components of automobile steering system are extremely complex in shape. It supports weight of car body, bears steering torque and braking torque during braking, and is an important safety component in harsh working environments. Requirements for organizational properties, mechanical properties and dimensions are extremely strict.

 

Current status of materials and forming processes
Aluminum alloy steering knuckles are mainly formed by casting technology, accounting for about 90%.

Design requirements and structural features
Structural features of parts: Functional areas should meet installation requirements between parts and connecting parts, such as through standard bolts, ball heads, etc.; interference requirements, minimum gap requirements between parts and peripheral parts should be met; strength requirements, should be through stress analysis , clarify key stress-bearing parts on parts; provide a basis for subsequent parts quality inspection. Technological requirements: parts should meet low-pressure casting process requirements.
Part performance requirements: static strength, durability, safety.

Role and performance requirements of subframe
A structural member on chassis of a car that connects suspension to body. Assembly bracket used to support axle and suspension, special functional structural component that carries engine and axle. Some parts also bear role of collision and collapse deformation. Its lightweight development can effectively reduce "unsprung mass", thereby improving energy efficiency, increasing cruising range and improving ride comfort. Usually, weight of a single steel subframe is 10~25kg. Using an aluminum subframe can achieve a weight reduction of 30~50%, and weight reduction effect is significant.
Current status of materials and forming processes
High-pressure vacuum integrated casting process - can reduce weight by about 40%

Other integrated casting processes

Casting + profile + welding process

Design requirements and structural characteristics of subframe
Structural requirements: 1. Subframe and car body are rigidly installed at four points; 2. It is equipped with a steering gear, stabilizer bar, control arm, and suspension installation position; 3. Clearance with surroundings meets general layout requirements; 4. A collapse structure is provided according to collision and space layout.
Part performance requirements: plate static strength, durability, safety, NVH.

 

3D model of aluminum alloy subframe
Design requirements and structural characteristics of Chang’an subframe
Structural features: 1. Rigidly connected to the car body; 2. Main structure is a "mouth" type structure, left and right front longitudinal beams and rear beams are low-pressure casting, and front cross beam is made of extruded aluminum; 3. There are two suspension mounting brackets at the front and rear; 4. A collapse structure is provided according to collision and space arrangement.
Structural features of cast rear beam: low-pressure casting of rear beam, thickness of casting is about 5mm, casting is a large-sized thin-walled complex part, thickness of main rib and web are both 4.5-6mm, and boss position for installation is thicker.