Surface state study of the pre-treatment process for electroless plated aluminum alloys for EP mandrels

Purpose: This study aimed to optimize the pre-treatment process for electroless nickel–phosphorus plating in the Einstein Probe project, addressing technical challenges encountered with 6061 aluminum alloy substrates to enhance coating quality and operational efficiency. Methods: Verification experiments were conducted using 6061 aluminum alloy sheets as substitutes for large aluminum mandrels. The effects of surface roughness, rinsing methods, and the necessity of acid pickling were systematically evaluated. The samples were characterized by scanning electron microscopy, atomic force microscopy, and energy-dispersive X-ray spectroscopy to analyze surface morphology and elemental composition. Results and Conclusion: Excessive surface roughness should be avoided, with a roughness below 338 nm ensuring uniform coatings. Flowing water rinsing after each step was critical to prevent contamination from residual solutions, whereas stagnant water immersion proved inadequate. Acid pickling was determined to be non-essential, as it had minimal impact on coating quality. The zinc layer formed during immersion exhibited weak adhesion and should be rinsed gently to avoid detachment. These findings offer valuable insights for pre-treatment process refinement in the Einstein Probe project and related applications.