The Role of Ni-P Coating Structure on Fly Ash Cenospheres in the Formation of Magnesium Matrix Composites

Abstract

The role of the Ni-P coating structure on fly ash cenospheres in the fabrication of magnesium matrix composites has been investigated. Two composites based on AZ91 commercial magnesium alloys with hollow aluminosilicate cenospheres were fabricated by the negative pressure infiltration technique. Two kinds of cenospheres (i.e., as Ni-P coated and after heat treatment) were used in order to determine the influence of the Ni-P coating structure on creating interfaces between the components. Microstructure analyses were carried out by light microscopy, atomic force microscopy, XRD, scanning, and transmission electron microscopy. Al 3 Ni 2 and Mg 2 Ni intermetallic phases at the component interfaces were formed in the composite with as-received Ni-P-coated cenospheres. After heat treatment of the Ni-P-coated cenospheres, NiO was created outside the external layer of the Ni-P coatings and this oxide remained stable at the component interfaces during composite fabrication. In both cases, the Ni-P coating prevented the reaction between the cenosphere walls and the magnesium matrix alloy, which contributed to obtaining intact cenospheres, unfilled by the matrix alloy.

Types of Component Interfaces in Metal Matrix Composites on the Example of Magnesium Matrix Composites

“…The cenospheres were used in the as-received state (uncoated), after Ni–P coating by the electroless plating method (i.e., with an Ni–P amorphous layer) and after Ni–P coating and heating at 773 K (i.e., with a crystalline Ni + Ni 3 P + NiO layer). These kinds of layers were described in previous works [ 9 , 22 , 49 , 50 ].…”

“…Due to the properties of the matrix itself, including its density, magnesium matrix composites constitute a modern group of materials, widely studied in many matrix-reinforcing phase systems. Several different magnesium matrix alloys (from the Mg–Al, Mg–Zn, or Mg–rare earth elements systems) with various reinforcing phases (various particles or fibers), for example, SiC, C gr , Al 2 O 3 , TiC, Ti, and fly ash microspheres etc., have been designed and investigated in recent years [ 1 , 2 , 3 , 4 , 8 , 9 , 10 , 11 , 12 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ]. Those composites are very attractive in applications such as the aerospace, automobile, or electronics industries due to their unique combination of different properties, e.g., exceptional dimensional stability and high damping capacity, specific strength and stiffness, or resistance to abrasive wear.…”

Compressive characteristics and low frequency damping of aluminium matrix syntactic foams

“…Moreover -like other metallic foams -AMSFs have good specific mechanical properties, which are isotropic contrary to liquid state produced 'conventional' metallic foams (because the lack of gravitational force effects, that has no role on the geometry of pores in the case of AMSFs). The matrix material of AMSFs is some kind of aluminium alloy usually; however, similar structures (in general metal matrix syntactic foams (MMSFs)) with steel [1,[3][4][5], magnesium [6][7][8][9][10][11][12][13], titanium [14][15][16][17] and zinc [18][19][20][21][22] matrices have also been reported. The filler or reinforcing hollow spheres can be ceramic or metallic in material and they are commercially available from specified providers, such as Hollomet GmbH [23], for example.…”

Mechanical and Microstructural Characterization of an AZ91–Activated Carbon Syntactic Foam

“…However, these fillers are susceptible to fracture and melt infiltration, which is amplified by a potential chemical reaction with the molten metal during casting. To decrease the proportion of fractured particles, cenospheres have been surface-coated to prevent their direct contact with molten magnesium [17]. However, this additional surface treatment increases the complexity and manufacturing costs.…”