Tailoring machinability and formability of an extruded Cu-Zn-Si alloy via heat treatment

초록

This study investigates the optimal heat-treatment condition for improving straightness during cold drawing while maintaining the strength and machinability of an extruded Cu-Zn-Si alloy. Particular attention is given to the evolution of the metastable x phase and its influence on residual stress and machining behavior. Heat treatment at 400 degrees C promotes the decomposition of the x phase into Cu3Si intermetallic compounds, whereas treatment at 600 degrees C induces a x-to-alpha phase transformation. The x-to-alpha transformation generates severe lattice distortion and increases internal residual stress, leading to deterioration of dimensional stability during drawing. In contrast, heat treatment at 400 degrees C for 1 h retains a moderate fraction of the x phase, facilitating chip segmentation, maintaining low cutting force, and suppressing residual stress development. As a result, this condition provides the optimal balance between machinability and dimensional stability, enabling improved straightness after drawing. These findings demonstrate that controlled x-phase evolution can effectively tailor the microstructure of Cu-Zn-Si alloys, highlighting their potential as high-machinability Pb-free brasses for industrial applications.

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