Microstructure, mechanical properties, and adhesion behavior of DLC/W coating on Al-Mg loudspeaker diaphragm for enhancing its acoustic performance

Abstract

Metal-based loudspeaker diaphragms show promise for high-frequency audio devices, but they produce sharp and fatiguing sounds. This study aimed to improve high-frequency response by depositing a durable diamond-like carbon (DLC)/W coating on aluminum‑magnesium (Al-Mg) diaphragms. The effect of PECVD deposition bias voltage on the coating's morphology, chemical structure, and mechanical properties was investigated. W-based intermediate layer boosted DLC-substrate adhesive strength by 2.5 times compared to direct DLC deposition. The nanohardness, elastic modulus, and Vickers hardness of DLC/W-coated diaphragms initially increased and then decreased with bias voltage (−100 to −300 V), peaking at −200 V, correlating with sp³ bond content. Compared to uncoated samples, the DLC/W-coated Al-Mg diaphragm loudspeakers expanded bandwidth by 2–5 kHz, improved performance gain by 3.5 dB, suppressed harmonic distortion to <6%, and enhanced subjective auditory experience. These findings hold potential for practical applications, advancing high-frequency loudspeaker technology.