Magnesium and its alloys with high strength-to-weight ratio, relatively high stiffness, good machinability and biocompatibility properties promise great potential as lightweight structural material in several sectors, such as automotive, aviation, space, military, energy, biomedical, etc. However, the poor surface mechanical properties and high chemical reactivity of magnesium alloys limit their widespread applications in aggressive environments. The rapid development of advanced magnesium alloys has renewed interest in specific magnesium alloy products for intended applications. In the last few decades considerable advances have been reported in the surface engineering strategies for magnesium alloys. The advanced methods not only protect the magnesium alloy parts against corrosion but also improve the mechanical, tribological, optical, thermal, and electrical properties of their surface. Last of twelve parts.
Market Overview
Magnesium alloys are used in a wide variety of structural and non-structural applications. There are several market survey reports for the forecast of magnesium metal for the period of 2020-2030. Though there are minor variations in terms of market size and annual growth rate projections, there is agreement in the growth trends. The global magnesium metal market is anticipated to grow because of the rising demand for lightweight components across automotive, aerospace, and infrastructure sectors. The global magnesium metal market size in 2021 was around 4 billion [1-6] US-Dollars, and it is predicted to grow around 6.6 billion US-Dollars by 2028 with a Compound Annual Growth Rate (CAGR) of about 8-10%. In terms of volume, cast alloys are expected to dominate the global magnesium alloys market during the forecast period. However, wrought alloys are projected to register a higher CAGR than cast alloys [5]. The followings are the salient points of key prospects and forecasts for magnesium alloys:
Drivers
The driving forces for growth of the magnesium market include:
- Availability of abundant natural resources, ease of products fabrication, recyclability, and extremely environmentally friendly attributes of magnesium are key driving factors for its sustainable growth.
- Rising popularity of magnesium alloys in consumer electronics due to their low weight and heat dissipation properties. The global electronics industry is projected to grow at a CAGR of about 6-7%. This will help in generating higher demand for magnesium alloys.
- Rapid expansion of the automotive industry which consumes a largest share of magnesium metal (~ 44%). The fast-growing adoption of electric vehicles with increasing support and incentives by the governments of many countries.
- The growth in the aerospace sector is expected because of extreme versatility, availability of a wide range of alloy products with specific properties for manufacturing of different parts. The rapid growth of aviation and space sectors in Asia and increased expenditure of various governments in the defence sector will push the demand for magnesium alloys. Further growth in this sector will be driven by technological innovations in magnesium products.
- Growing interest for magnesium alloys in medical implants and prosthetics due to their biocompatibility characteristics.
- Increasing demand of specific magnesium alloys in the construction sector due to their non-toxic, and flame-retardant properties.
Restraints
The factors restricting the usage of magnesium alloys are high costs of production, poor corrosion resistance, limited workability at ambient temperature, low elongation, and insufficient creep resistance at elevated temperatures. However, there are ample ongoing efforts to mitigate most of these issues.
Regional Analysis
During the forecast period, the global magnesium market will be dominated by Asia-Pacific [2,3]. This region will account for a volume share of above 68 % owing to rapid industrialization, coupled with growing automotive and aviation sectors across key markets including China, India, Japan, South Korea and Taiwan [5].
The region wise magnesium alloy market, and application segment overview over the years is presented in Figures 1 and 2.
Fig. 1: The magnesium alloy market is dominated by customers from the Asia Pacific region - Graphics: Grandview Research
Fig. 2: By 2029, the share of magnesium in automotive, aerospace and defense is expected to increase significantly - Graphics: Maximize Market Research
Prospects and Forecasts
The light-weight, high specific strength, good castability and excellent machinability make magnesium alloys a promising engineering material for a variety of applications where weight reduction is a significant factor [7]. The present increased confidence of magnesium alloys can largely be traced to the development of more corrosion resistant alloys. Though magnesium casting is still the major market due to ease of fabrication of complex parts, applications of forgings with new innovative techniques are continuously increasing, as the latter ensure better mechanical and functional properties. Of late, many innovative techniques for magnesium alloys forging and tools have been developed.
The most critical shortcoming of magnesium and its alloys which restrict their widespread usage is their poor corrosion resistance [8]. With the exception of a very few, all-industrial applications of magnesium alloys require suitable surface protection. Magnesium and its alloys are categorised as “difficult substrates” for electrochemical deposition due to their high chemical affinity for aqueous solutions. Magnesium dissolves readily as Mg2+ in all solutions with a pH < 10. Magnesium reacts with atmospheric oxygen and water, resulting in the formation of an instant oxide-carbonate film on the surface. Unlike aluminium, this film is highly porous, powdery, and not self-healing; consequently, it does not offer protection. On the contrary, it prevents the formation of good bonding of subsequent coatings on the substrate. To ensure good adhesion, this film must be removed, before proceeding to any coating deposition. Nevertheless, in the last few decades considerable advances have been reported in the area of surface protection of magnesium alloys. By selecting the appropriate combination of alloy, and surface modification techniques, the usage of magnesium alloys can be greatly enhanced.
A large number of surface treatment processes are available for magnesium alloys, but only few have actually attained commercial importance. In general, the chemical immersion processes, viz., chrome pickle, dichromate treatment, dilute chromic acid treatment, chromate conversion coating, chrome-manganese conversion coating, and phosphate treatment, provide poorer corrosion protection and abrasion resistance than the electrolytic processes. These processes can only be used for temporary protection during shipment and storage or as a good base for subsequent coating/paint application. Galvanic black anodizing which imparts high absorptance and thermal emittance can be used as a flat absorber for thermal control applications in mild corrosive environments.
Modified caustic anodizing films provide improved resistance to corrosion and wear. Modified acid fluoride anodizing, and micro arc oxidation processes offer far superior corrosion resistance. Modified acid fluoride anodizing with high solar absorptance (0.84) and IR emittance (0.88) is found suitable for spacecraft thermal control applications. A thick micro-arc-oxide film significantly enhances the hardness, thermal resistance, dielectric strength, friction coefficient, and wear and corrosion resistance of the substrate. The corrosion performance of different coatings on magnesium alloys was found in the following order: modified acid fluoride > micro arc oxidation-phosphate > micro arc oxidation-silicate > dichromate > Galvanic black anodizing > phosphate-permanganate > bare magnesium [9].
Black micro arc oxidation coatings with high emittance > 0.95 have great significance in thermal control applications and to suppress the unwanted reflections or scattered light in optical systems. Development of high corrosion resistance electroless nickel plating after double zincating has paved the way for ease of subsequent plating of copper, silver, gold etc. [10]. Multilayer coatings of different materials, and technologies (conversion coatings, anodic oxidation, gas-phase deposition, powder/polymer coatings, electrolytic / electroless plating, etc.) may synergetically improve the corrosion resistance and requisite functional properties. The typically, multilayer surface treatment consisted of chemical conversion or anodizing followed by top paint coating, but there can be exploration of a wider range of multilayer coating options including composite coatings.
Conclusion
The consumption of magnesium alloys in a global market is expected to grow by 8-10% every year. This is driven mainly by the automotive sector, to save the energy cost, and increase in the number of electrical vehicles in particular. The share of the aerospace sector which is still just above 1% is a serious concern. This is not only because this sector has potential for growth, but it has a high stake of reliability. The increase in consumption of magnesium alloy products in the aerospace sector will open the avenues of technological innovations and drive the confidence of others sectors.
Though the efforts have been continuing, there exists an urgent need for focused accelerated efforts to develop advanced magnesium alloys with superior mechanical and corrosion resistance properties to provide further impetus for the commercial exploitation of this designer’s favourite material. Also, there is the necessity of detailed studies in surface engineering to establish the robust surface modification techniques that can ensure long-term corrosion protection in adverse service conditions along with requisite functional properties.
REFERENCES:
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