Laser coating as a potential coating fabrication of magnesium alloys

In a recent study published in the journal MetalsSpanish researchers conducted a state-of-the-art investigation of key process parameters of magnesium laser coating to understand the effect of different coating-substrate systems on mechanical and corrosion resistance properties.

Study: An Introduction to Laser Plating Coatings on Magnesium Alloys. Image Credit: Juergen Faelchle/Shutterstock.com

Magnesium alloys and laser coating

Magnesium alloys are good structural materials due to their low density, which results in very high specific mechanical properties, ease of machining and low cost. The main constraints of magnesium alloys are their poor surface characteristics and their poor resistance to wear and corrosion. One strategy to overcome these constraints is to use laser coating techniques to create protective surface coatings.

Different methods of cladding laser feeding: (a) paste feeding;  (b) powder injection;  (c) wire feed;  (d) preplaced powder [6].

Different laser cladding feeding methods: (a) pulp feed; (b) powder injection; (vs) wire feed; (D) preplaced powder. Riquelme, A et al., Metals

The main advantages of laser coating over traditional approaches include reduced thermal distortion of the substrate, improved surface attributes with low dilution, and improved surface quality. To obtain coatings with good mechanical properties, it is necessary to choose the appropriate process parameters (laser power, powder feed, scanning speed and properties of the substrate and powder)

Laser manufacturing methods are divided into three types: laser plating, laser alloying, and laser glazing. Laser coating is a coating manufacturing technology that uses a laser as an energetic material to generate low porosity and enhanced coatings on metals. Laser alloy technology simultaneously simulates the feed material and the substrate, resulting in a homogeneous alloy metal. The laser glazing only melts a small part of the substrate and cools quickly, resulting in amorphous crystals.

This study examines current magnesium laser cladding processes and investigates the effect of the most critical manufacturing parameters on the interaction of various coating-substrate systems used on mechanical properties and corrosion resistance.

Methodology

The coating process was carried out using a laser coating system, which includes a laser (diode laser or Nd:Yag laser or CO2 laser), excimer laser and a feed material, which is sprayed with a carrier gas and coaxial with the laser beam. The feed material is a spherical powder sprayed with a carrier gas through a coating nozzle. The coating nozzle laser is connected to a motor control system, usually consisting of a CAD (computer aided drafting) system and a motion robot or xy motion table.

Inputs, outputs and process parameters of laser coating [6].

Inputs, outputs and process parameters of laser coating. Riquelme, A et al., Metals

Effect of process parameters

According to the various studies, the input parameters have an impact on the laser cladding of magnesium alloys and to obtain high quality coatings, the optimal combination of scanning speed and laser power must be determined. Coating geometry, dilution, melting, and heat affected zones are all affected by focal position on the substrate surface. The wavelength of the laser beam has a significant impact on the reflectivity-absorptivity of the metal. The energy absorbed by the substrate expands the dilution zone, affecting the microstructure and characteristics of the coating.

The output parameters of the laser coating are determined by the input factors such as dilution ratio, coating geometry, and the existence of cracks and pores, which are mainly governed by the laser, the motion device, and the characteristics of the feed material.

Most pure metal, binary and ternary alloy coatings include Mg-Al because Al increases the hardness of Mg; however, adding Al to Mg alloys reduces corrosion performance. The presence of Al allows some of the generated phases to conform to the Al-Mg equilibrium phase diagram, and the presence of other metals causes the formation of Al-metal or Mg-metal phases.

Investigation of High Entropy Alloy (HEA) coatings (AlCoCrCuFeNi coatings) on pure magnesium reveals that dilution between substrate and coating allows detection of CuMg2 dendrites.

Studies on the fabrication of ceramic coatings on magnesium alloys suggest that ceramics have a low affinity to react with the magnesium substrate, form other compounds, refine the substrate microstructure, and improve resistance to wear and corrosion. substrate corrosion.

conclusion

Researchers investigated the effect of process parameters on magnesium laser coating. According to the researchers, the most studied matrices are aluminum-based alloys, and frequently used ceramic reinforcements have a particulate morphology because these composite coatings combine improved tribological properties and high corrosion resistance.

Understanding how different coating manufacturing parameters affect the final surface properties of magnesium alloys is essential for their use in a wide range of manufacturing situations. In the future, several processes such as welding with laser cladding or three-dimensional printing with direct laser deposition can be integrated as an extension of the laser cladding process.

The references

Source: Riquelme, A.; Rodrigo, P. An Introduction to Laser Plating Coatings on Magnesium Alloys. Metals 2021, 11, 1993. https://www.mdpi.com/2075-4701/11/12/1993

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