Hyper-eutectic al-si alloy coating respectively an al-si composite

摘要

A hypereutectic aluminium-silicon alloy or aluminium-silicon composite material coating has a heterogeneous structure of an aluminium solid solution, intermetallic phases such as Mg2Si, oxides and (i) silicon precipitates, (ii) embedded silicon particles or (iii) silicon precipitates and embedded silicon particles, the mean size of the primary silicon precipitates or embedded silicon particles being less than 10 mu m, the mean oxide size being less than 5 mu m and the coating being mainly copper-free, i.e. the copper content is less than 1 (preferably less than 0.1, especially less than 0.01) wt.%. Also claimed are processes for producing the above coatings by thermal (especially atmospheric plasma) spraying with parameters adjusted for formation of oxides. Preferably, the spraying material has the composition (by wt.) (A) (for coating type (i)) 23-40 (especially 25)% Si, 0.8-2.0 (especially 1.2)% Mg, NOTGREATER 0.6% Zr, NOTGREATER 0.25% Fe, NOTGREATER 0.01% each of Mn, Ni, Cu and Zn and balance Al; (B) (for coating type (i)) as (A) but containing 23-40 (especially 25)% Si, 1-5 (especially 4)% Ni and 1.0-1.4 (especially 1.2)% Fe; (C) (for coating type (ii)) 5-50% Si particles and 50-95% alloy particles of composition (A) but containing 0-11.8 (especially 9)% Si; (D) (for coating type (ii)) 5-50% Si particles and 50-95% alloy particles of composition (B) but containing 0-11.8 (especially 9)% Si; (E) (for coating type (iii)) 5-50% Si particles and 50-95% alloy particles of composition (A) but containing 11.8-40 (especially 17)% Si; or (F) (for coating type (iii)) 5-50% Si particles and 50-95% alloy particles of composition (B) but containing 11.8-40 (especially 17)% Si.