**1. Introduction**

Magnesium alloys are ranked among the lightest constructional metallic materials [1,2]. They find their application in the automotive and aerospace industry due to their low density and high value of specific strength, toughness, and good machinability [3]. Low corrosion resistance, high chemical reactivity, low hardness, and low wear and abrasion resistance are considerable disadvantages of magnesium-based materials [4].

Mg–Zn–RE-based magnesium alloys such as ZE10 and ZE41 achieve higher values of strength and better mechanical and corrosion properties in comparison with pure magnesium [2,5]. These alloys contain, besides Mg, Zn, and rare earth (RE) elements, Pr, Nd, La, Ce, and a small amount of Zr [1]. Zinc improves the strength and corrosion resistance of magnesium alloys. Rare earth elements improve the casting and mechanical properties (strength and creep resistance) of the alloys at higher temperatures. Zr is mainly used for grain refinement [1,6]. Although these alloys achieve better mechanical and corrosion properties in comparison with pure magnesium, their surface properties such as hardness, corrosion, and wear resistance are still inadequate for certain industrial applications.

There are several ways to improve magnesium alloys surface properties and resistivity, including galvanic or electroless deposited coatings, thermally sprayed coatings, and applications of conversion coatings [7,8].

One way to protect the material from corrosion, and improve the material surface's mechanical properties, is to apply electroless Ni–P coatings in a nickel bath [9]. Electroless deposited Ni–P coatings increase corrosion resistance as well as the surface's mechanical properties such as hardness and wear resistance. Applied low-phosphorus Ni–P coatings, compared with high-phosphorus Ni–P coatings, have a high value of hardness, a high density, and a high crystallinity [10]. However, the deposited high-phosphorus Ni–P coatings have higher corrosion resistance when compared to the low-phosphorus Ni–P coatings. Based on the phosphorus content in Ni–P coatings, low-, medium-, and high-phosphorus Ni–P coatings can be distinguished. Low-phosphorus Ni–P coatings contain 2–5 wt % phosphorus, medium-phosphorus Ni–P coatings contain 6–9 wt % phosphorus, and high-phosphorus Ni–P coatings contain >10 wt % phosphorus [9,11].

In [12], the corrosion behavior of three types of electroless deposited Ni–P coatings was studied. Ni–P coatings deposited on the mild steel contained 3.34% P (low phosphorus), 6.70% P (medium-phosphorus), and 13.30% P (high phosphorus). Based on the obtained results of potentiodynamic polarization tests and Nyquist plots of deposited Ni–P coatings in a 3.5% NaCl solution, it was determined that corrosion potentials and charge transfer resistances (in this case, equal to the polarization resistance) of deposited Ni–P coatings increased as phosphorus content increased. Corrosion potential *E*corr of the low-phosphorus Ni–P coating obtained using the Tafel extrapolation method was −536 mV, and charge transfer resistance *<sup>R</sup>*ct was 6.90 kΩ·cm2. Corrosion potentials for medium- and high-phosphorus Ni–P coatings were −434 mV and −411 mV, respectively. Charge transfer resistances of medium- and high-phosphorus coatings were 24.86 kΩ·cm2 and 37.45 kΩ·cm2, respectively.

The adhesion of the coating to the substrate has a great influence on corrosion behavior and the mechanical properties of Ni–P coatings deposited on the substrate [10]. The adhesion of the Ni–P coating to the deposited substrate is significantly affected by appropriately selected pre-treatment of the substrate surface, such as grinding, blasting, degreasing, pickling, and interlayer deposition. [7,9,13]. A very frequent type of pre-treatment is zincate-zinc immersion [14–16], but the main disadvantage is the high pH value [14–17]. Zinc immersion is used to remove residual oxides and hydroxides from the surface of the substrate [14].

This paper deals with the preparation and characterization of an electroless deposited Ni–P coating deposited on a wrought ZE10 magnesium alloy. This study is focused on the measurement and evaluation of mechanical, physical, and corrosion properties of the coated substrate, while a specific pre-treatment was used before substrate coating. The mechanism of the corrosion attack and the corrosion resistance of the coated and plain material in 0.1 M NaCl were studied using potentiodynamic tests and immersion tests, and the results were analyzed in terms of light microscopy and scanning electron microscopy.
