Characterization of Ni-P coating prepared on a wrought AZ61 magnesium alloy via electroless deposition

Abstract

A low-phosphorous Ni-P coating was prepared on a wrought AZ61 magnesium alloy via electroless deposition for 1 h after an adequate substrate-surface pre-treatment. The prepared coating with a thickness of 10 μm was characterized by the uniform distribution of Ni (95.4 % mass fraction) and P (4.6 % mass fraction) in the cross-section. Microcavities present in the coating resulted in quite a low corrosion resistance of the coated magnesium alloy in a 0.1 M NaCl solution. On the other hand, the coating exhibits a high degree of adhesion, as evidenced by a scratch test, and significantly improves the AZ61 magnesium-alloy microhardness. Keywords: electroless nickel, magnesium alloy, AZ61, characterization of Ni-P coatings Malo porozna Ni-P prevleka je bila pripravljena na povr{ini kovane AZ61 magnezijeve zlitine. Prevleka je bila pripravljena z enourno neelektri~no depozicijo na predhodno ustrezno obdelani povr{ini zlitine. Pripravljena prevleka debeline 10 μm je imela v pre~nem prerezu enakomerno porazdelitev Ni (95,4 % masnih odstotkov) in P (4,6 % masnih odstotkov). Zaradi prisotnosti mikropraznin v izdelani prevleki je korozijska odpornost prevle~ene magnezijeve zlitine v 0,1 M NaCl raztopini slaba. Preizkusi razenja prevleke pa so po drugi strani pokazali zelo dober oprijem izdelane prevleke s povr{ino zlitine in znatno izbolj{anje mikrotrdote AZ61 magnezijeve zlitine.

Characterization of Electroless Ni–P Coating Prepared on a Wrought ZE10 Magnesium Alloy

“…The high concentration of inter-column defects, such as microvoids and micropores, [26,27], form channels where the corrosion ions and environment can pass through the coating and react with the substrate. The presence of microcavities was not evident between nodular cusps of the deposited coating (Figure 2b), which is in agreement with observations in [28]. Based on an evaluation of SEM figures (Figures 2b and 3a), no defects and cracks were observed in the deposited Ni-P coating at the ZE10 magnesium substrate/Ni-P coating interface.…”

“…), experimental parameters (tip and scratch rate), and properties of the substrate-layer system (thermal coefficients, microstructure and internal stresses, elasticity, and hardness modules). Figures 4 and 5 show the scratch track morphology and the layer cracking character, which is similar to the case of Ni-P coatings on AZ31 and AZ61 magnesium alloys presented in [28,30].…”

“…The formation of transverse tensile arch cracks [22,34] across the entire width of the track was observed (Figure 4). The adhesion strength of the experimental electroless deposited Ni-P coating on a wrought ZE10 magnesium alloy (L c1 and L c2 ) was higher compared to the data presented in articles [28,30], where the Ni-P coating was deposited on AZ31 and AZ61 magnesium alloys, respectively. The difference could be explained by the coated substrate pre-treatment process.…”

“…The EDS analysis determined that the Ni content in the deposited Ni-P coating was 95.6 wt % and the P content was 4.4 wt %. Based on the literature [9,29], it was determined that the deposited Ni-P coating is low-phosphorus, as in the cases of the AZ31 magnesium alloy presented in [30] and the AZ61 magnesium alloy in [28]. Deposited Ni-P coating with an average thickness of about 10 µm was chosen for EDS analysis (Figure 3).…”

“…The difference could be explained by the coated substrate pre-treatment process. The pre-treatment of AZ31 and AZ61 magnesium alloys before the deposition of the Ni-P coating included polishing to a roughness R a ≈ 0.25 µm [28,30]. However, the surface of the experimental ZE10 magnesium alloy was polished to a roughness R a ≈ 2 µm, which is significantly rougher than AZ31 and AZ61.…”