This paper provides a review of recent developments in the field of Mg corrosion and puts those into context. This includes considerations of corrosion manifestations, material influences, surface treatment, anodization, coatings, inhibition, biodegradable medical applications, stress corrosion cracking, flammability, corrosion mechanisms for HP Mg, critical evaluation of corrosion mechanisms, and concluding remarks. There has been much research recently, and much research continues in this area. This is expected to produce significantly better, more-corrosion-resistant Mg alloys.

Review of Recent Developments in the Field of Magnesium Corrosion

https://bura.brunel.ac.uk/bitstream/2438/13101/1/FullText.pdf

Cold spraying - A materials perspective

Microstructure and corrosion performance of a cold sprayed aluminium coating on AZ91D magnesium alloy

Cold spray is a fast growing coating process involving in high strain rate deformation of spray particles. Early investigations stressed the retaining of feedstock microstructures into deposits. However, in recent years, metastable microstructures including high density of dislocations, nanosized grains and localized amorphous phase have been frequently observed through detailed microstructure characterization and it was found that those metastable microstructures remarkably affect the coating properties. In this review article, the evolution mechanisms of metastable microstructure in a cold spray coating during deposition of spray particles were examined in terms of in-situ densification, residual stress, dislocation multiplication, grain refining, phase transformation and amorphization through typical materials. Feedstock microstructure design, in-process control and material selection are essential approaches to acquire the coatings with desired microstructure.

High velocity impact induced microstructure evolution during deposition of cold spray coatings: A review

Al–Al 2 O 3 composite coatings were produced on AZ91D magnesium alloy substrates using kinetic metallization (KM), which is a special type of cold spray using a convergent barrel nozzle to attain sonic velocity. The effect of the volume fraction of Al 2 O 3 particles and KM spray temperatures on the microstructure, hardness of the composite coatings, the deposition efficiency, and the bond strength between the coating and substrate was studied. Results show that addition of Al 2 O 3 particles not only significantly improves the density of the coating, but also enhances the deposition efficiency to an optimum value. The bond strength of the composite coatings with the substrate was found to be much stronger than the coating itself, measured using a specially designed lug shear method. Furthermore, based on bond strength data and SEM analysis, higher Al 2 O 3 content resulted in a failure mode transition from adhesive failure to cohesive failure. This is considered a result of a competition between the strengthening of the ceramic reinforcing particles at the coating/substrate interface, and the weakening of coating cohesive strength due to an increase in the proportion of weaker Al–Al 2 O 3 bonds compared with stronger Al–Al bonds. Characterisation of the composite coating in terms of hardness, porosity and microstructure was also conducted.

The influence of ceramic particles on bond strength of cold spray composite coatings on AZ91 alloy substrate

Effect of α-Al2O3 on the properties of cold sprayed Al/α-Al2O3 composite coatings on AZ91D magnesium alloy

The invention relates to a preparing technology of metal composite coating, in particular to a coating preparing method and device by mixing metal and plastic powders. The aerodynamic spraying technology is adopted in the invention: metal and plastic powders are mixed; part of compressed air which carries powder when passes a powder feeder and gas preheated by a heater is mixed at an air inlet of a supersonic flow nozzle and then the mixed gas passes the nozzle to develop a gas-solid two-phase flow; solid particles in the gas-solid flow are sprayed on the surface of a workpiece and then develop serious plastic deformation and deposit on surface of the workpiece; and subsequent high kinetic energy particles repeat the above process to form alloy or coating. The method has the advantages of simple structure, low cost and high efficiency and can be applied to composite coating preparation. The device is provided with a high-pressure air source, the heater, the powder feeder, and the supersonic flow nozzle, wherein the high-pressure air source is connected with an air inlet pipe; and the air inlet pipe is connected with the supersonic flow nozzle through the powder feeder and the heater respectively. The device has the advantages of simple structure and strong practicability.

Coating preparing method and device by mixing metal and plastic powders

Different proportions of α-Al2O3 and pure Al powders were coated onto AZ91D magnesium alloy substrates by cold gas dynamic spray. The microstructure and morphologies of the coatings were observed by scanning electron microscope. The friction and wear properties were tested by a ball-on-disk wear tester. It was found that the interfaces between grains and substrates formed close boundaries. It is revealed that the composite coatings could increase the friction or wear properties of the coatings. It was observed that the wear of coatings was converted from adhesive wear into abrasive wear with α-Al2O3 particles increasing and that the adhesive wear accompanied with abrasive wear would increase the wear rate of coatings.

/pdf/friction-and-wear-properties-of-cold-gas-dynamic-sprayed-a-3j3mz6z8pe.pdf

Friction and Wear Properties of Cold Gas Dynamic Sprayed α-Al2O3-Al Composite Coatings

The invention discloses a cold spraying device and a method for preparing a 316L stainless steel coating, and belongs to the cold spraying technical field. The device mainly comprises a control system, a powder feeder, a gas heater, a laval nozzle and a powder heater. One end of the gas heater is connected with the laval nozzle, and the other end of the gas heater is connected with the powder feeder. One end of the powder feeder is connected with the control system, and the other end of the powder feeder is connected with one end of the powder heater. The other end of the powder heater is connected with the laval nozzle. In preparation of 316L stainless steel coating by utilization of the device, the technological parameters are as follows: the carrier gas preheating temperature is 200-600 DEG C, the spraying distance is 10-30 mm, the spraying pressure is 1.5-2.5 MPa, and the powder-feeding heating temperature is 200-500 DEG C. The modified cold spraying device heats the stainless steel powder from the powder feeder, and a compact stainless steel coating tightly combining with a matrix is obtained.

Yongshan Tao

Papers

Microstructure and corrosion performance of a cold sprayed aluminium coating on AZ91D magnesium alloy

Effect of α-Al2O3 on the properties of cold sprayed Al/α-Al2O3 composite coatings on AZ91D magnesium alloy

Coating preparing method and device by mixing metal and plastic powders

Friction and Wear Properties of Cold Gas Dynamic Sprayed α-Al2O3-Al Composite Coatings

Cold spraying device and method for preparing 316L stainless steel coating