Al Alloys and Manufacturing Processes for Lightweight Applications in Electric Vehicles

Abstract.

Due to increasing environmental concerns, battery-powered electric vehicles (BEV) have gained popularity in the automotive for the past few years. An induction motor is an essential component of the propulsion system in integrated BEVs working on different operating conditions [1]. Since a rotor of the induction motor is configured with an electrical sheet, a rotor bar, and end-ring (Fig. 1), which are usually manufactured by high-pressure die casting (HPDC) processes. Figure 2a presents an illustration of a cold-chamber high-pressure die casting machine. The process starts with ladling the liquid metal into the shot sleeve for each cycle. Die cavity and plunger tip normally are sprayed with an oil or lubricant to provide protection from severe degradation. This increases the die material’s life and reduces the adhesion of the solidified component. The cycle using the cold-chamber high-pressure die casting process as a model is shown in Fig. 2b. In a cycle, liquid metal is ladled into an injection system (i), which is then immediately pushed (ii) through a sleeve and runner system (iii) into a die cavity at a very high speed (iv), and a high pressure is applied for intensification. High pressures are maintained on the alloy during solidification. After complete solidification, the die opens (v) and finally the component is ejected (vi) [2]. To obtain the high efficiency of an induction motor, a heavy transition metal, copper, having a high electrical conductivity and low resistivity is often used [3]. For weight reduction of the BEVs with extended range, however, aluminum with a density of 2700 kg/m³ and a melting temperature of 660 °C as a lightweight metal is strongly advocated by the automotive industry to replace heavy Cu. This is because Al is over two times lighter than copper. Its low melting point compared with that of Cu makes Al and its alloys easy to be manufactured for components in the induction motor via casting processes such as high-pressure die casting [3].

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