Magnesium Alloy Classification

2️⃣Magnesium-aluminum Alloy and Aluminum-magnesium Alloy

(1) Magnesium-aluminum alloy contains up to 90% magnesium, with the remaining 10% consisting of approximately 9% aluminum, 1% zinc, and trace amounts of elements like manganese, silicon, and zirconium. Adding small amounts of aluminum or other metals enhances its hardness, strength, and casting properties.

(2) Aluminum-magnesium alloy contains up to 94% aluminum and only 5% magnesium, with the remaining 1% comprising chromium, iron, and other elements. Adding a small amount of magnesium or other metals increases its hardness, making it several times harder than other aluminum alloys.

(3) Table 1 compares the properties of typical magnesium-aluminum and aluminum-magnesium alloys for both non-structural and structural components:

For non-structural parts, magnesium-aluminum alloy offers advantages in lightweight design, heat dissipation, impact resistance, electromagnetic shielding, and cutting efficiency compared to aluminum-magnesium alloy. However, aluminum-magnesium alloy excels in surface treatment and cost-effectiveness.

For structural components, magnesium-aluminum alloy is about one-third lighter than aluminum-magnesium alloy for the same structural dimensions. However, aluminum-magnesium alloy exhibits approximately one-third greater load-bearing capacity. Yet, its relatively lower fatigue strength could reduce the lifespan of structural components. Additionally, its lower elastic modulus and stiffness make it effective for absorbing vibrations.

From the comparison, it's evident that magnesium-aluminum alloy holds significant advantages for non-structural applications. Notable alloys in this category include AZ31B, AZ91D, and AZ80A, with AZ31B being widely used due to its mature production technology, moderate performance, and cost-effectiveness.

In the aluminum-magnesium alloy, the No.5 series alloys belong to the aluminum-magnesium deformation alloys. No.5 series alloys cannot be strengthened through heat treatment but are usually strengthened through work hardening. The No.6 series aluminum alloys primarily consist of magnesium and silicon, with the main strengthening phase being Mg2Si, allowing for heat treatment strengthening.

Improvements in microstructure control through new processing routes, such as HPR, ECAP, ATMP, and studying their impact on ductility, result in high-toughness magnesium-aluminum alloys. Various methods like surface slip, accelerated lateral slip, weak base textures, and microstructure refinement significantly enhance the ductility of magnesium alloys. Current products of AZ31B exhibit tensile strengths of 300-350 MPa for extruded rods and 280-300 MPa for extruded profiles in the H112 state, with elongation rates ranging from 15-25% and 18-20%, respectively. It's expected that magnesium-aluminum alloys will replace No.6 series aluminum-magnesium alloys, becoming the most widely used efficient materials for non-structural and structural purposes. Moreover, the maturation of surface treatment technologies and cost reductions indicate promising market prospects.

 Table1 typical Mg-Al alloy and Al-Mg alloy properties

3️⃣RE-containing Magnesium Alloy

1、RE-containing magnesium alloy

RE-containing magnesium alloy generally refers to magnesium alloys containing rare earth elements. The rare earth elements include Y, Ce, Nd, Gd, and La elements. Due to their unique electron distribution outside the nucleus, rare earth elements have a large solid solution in magnesium. It has good solid solution strengthening and precipitation strengthening effects; it can effectively improve the structure and microstructure of the alloy, improve the mechanical properties of the alloy at room temperature and high temperature, and enhance the corrosion resistance and heat resistance of the alloy; the atomic diffusion ability of rare earth elements is poor, and the Increasing the recrystallization temperature and recrystallization process of magnesium alloys has a significant effect; rare earth elements also have a good aging strengthening effect, which can precipitate very stable dispersed phase particles, which can greatly improve the high-temperature strength and creep resistance of magnesium alloys. Therefore, a series of RE-containing magnesium alloys have been developed in the field of magnesium alloys, so that they have high strength, heat resistance, corrosion resistance, and other properties，effectively expanding the application field of magnesium alloys.

2. Main three types of RE containing magnesium alloy

2.1 Heat-resistant RE containing magnesium alloy The addition of rhenium RE into the Mg-Al alloy can effectively increase the high-temperature performance and creep strength of the Mg-Al alloy; the addition of Ce-rich mixed rare earth to the Mg-Al alloy can effectively improve the alloy's performance. The addition of rare earth elements in Mg-Zn alloys can improve the casting properties and creep resistance of the alloys, and the addition of RE in Mg-Li alloys improves Mg-Li through solid solution strengthening and the formation of finely dispersed intermetallic compounds. The mechanical properties of the alloy can also increase the recrystallization temperature of the alloy and promote the age hardening of the Mg-Li alloys.

2.2 Rare earth flame retardant magnesium alloy Rare earth elements can improve the flame retardant properties of magnesium alloys, and it increases with the addition of rare earth elements. The addition of Ca, Be,and other elements to magnesium alloys can increase the ignition point by about 200 ℃ to 250 ℃; the addition of Ca makes the alloy grains coarse and the mechanical properties deteriorate, but at the same time adding an appropriate amount of rhenium RE can weaken this adverse effect.

2.3 High-strength rare-earth-magnesium alloys Rare earths have a significant strengthening effect on magnesium alloys, and the microscopic mechanism of rare-earth element strengthening and toughening is explored, and the development of high-strength and high-toughness rare earth-magnesium alloys is a hot spot in magnesium alloy research.

neodymium Nd to the magnesium alloy can strengthen the matrix of the alloy, improve the heat resistance strength of the alloy, and make the casting structure dense. Adding gadolinium Gd and yttrium Y to magnesium alloys can significantly improve the strength of magnesium alloys.

3. The trend of RE containing magnesium alloy in terms of high-performance magnesium alloys, both the magnesium alloys that have been used in commercial applications and those under development; and the ultra-high-strength magnesium alloys that are rapidly solidified under extreme conditions are all related to rare earth elements. The scientific community believes that the history of research and application of magnesium alloys is the history of research and application of RE-containing magnesium alloy.

Rare earth magnesium alloy is a high-performance magnesium alloy with low density, high specific strength, high specific stiffness, good shock absorption, corrosion resistance, easy processing, and easy recycling. Engineering Structural Materials. A large number of applications have begun in the aerospace, military industry, electronic communication, transportation, and other fields.

China is rich in magnesium and rare earth resources. It is not only a big producer of magnesium and magnesium alloys; but also a big producer of rare earths. In the context of the global shortage of iron, aluminum, zinc, and other metal resources, China is making use of rich rare earth resources to promote RE-containing magnesium alloy. development has unique advantages.

4. Supply of RE containing magnesium alloy

Two rare earth magnesium alloys are specially listed in the Chinese aviation standard and national standard, and they can work at 150-250 ℃ for a long time. One is the rare earth zirconium magnesium alloy ZM3, with rare earth Ce as the main component. The alloy is usually in an as-cast and T2 state, and its typical mechanical properties are σb=140MPa, σ0.2=90 MPa, δ=2.5%; below 250 ℃ σb=130MPa, σ0.2=30MPa. The other is magnesium-zirconium-neodymium alloy ZM6. ZM6 can be widely used in high-strength parts at room temperature and below 250 °C due to its comprehensive performance superior to ZM3 alloy. Moreover, the alloy has good casting properties, low hot cracking tendency, and good filling ability, so it is a high-quality magnesium alloy with wide application prospects.

In addition, Aikerly can supply ZE61, MB22, AE80, WE43, WE54, VW63, VW94, and other high-strength heat-resistant containing RE-magnesium alloys. The room temperature tensile strength of cast magnesium rare earth alloy can reach more than 320MPa, which makes up for the defect of low strength and poor plasticity of cast magnesium alloy. It can meet the demand of different customers for high-performance alloys.

4️⃣Wrought Magnesium Alloy and Cast Magnesium Alloy

Industrial magnesium alloys can be divided into two categories: cast magnesium alloys and wrought magnesium alloys, which are divided according to the production process of magnesium alloys.

1. Cast magnesium alloy.

Magnesium alloys can be formed by sand casting, investment casting, die casting, semi-solid casting, etc. Among them, magnesium alloy die casting new technologies vacuum die casting and oxygen-filled die casting, the former has successfully produced AM60B magnesium alloy automobile wheels and steering wheels, the latter has also begun Used in the production of magnesium alloy parts for automobiles. The new technology of semi-solid thixotropic casting, the microstructure and mechanical properties of magnesium alloy products produced by this method are better than ordinary die-casting products, and have been successfully industrialized worldwide.

1.1. Common cast magnesium alloys: ①Mg-Al-Zn. ②Mg-Zn-Zr③Mg-Zn-AI, Mg-Zn-Al-Ca ④Mg-RE Mg-RE-Mn

1.2. Die casting magnesium alloy:

1) ①Mg-AI-Zn (AZ91) ②Mg:AI-Mn (AM50, AM60) ③Mg-Al-Si (AS41, AS21)

④Mg-AI-RE (AE42) @Mg-AI-Ca (AX51) : Mg-AI-Ca-RE (ACM522) and Mg-Zn-Al-Ca

2) Mg-RE-Zn (MEZ)

2. Wrought magnesium alloy:

Wrought magnesium alloys refer to magnesium alloys that can be processed by plastic forming methods such as extrusion, rolling, forging and stamping.

①Forging ②Extrusion: 1.Mg-Al-Zn2 Mg-Zn-Zr3.Mg-Zn-Mn 4.Mg-Mn 5.Mg-Li Mg-Li-AI Mg-Li-Al-MM and Mg-L -Al-SiI③ rolling

There is no strict distinction between cast magnesium alloys and wrought magnesium alloys. Cast magnesium alloys AZ91, AM20, AM50, AM60, AE42, etc. can also be used as wrought magnesium alloys.

There is a big difference between the two in terms of composition, structure and properties. Cast magnesium alloys are produced by die-casting process, which is characterized by high production efficiency, high precision, good surface quality of castings, excellent as-cast structure, and can produce thin-walled and complex shapes. 

Compared with cast magnesium alloys, wrought magnesium alloys have higher strength, better plasticity and more diverse specifications.

5️⃣Magnesium-manganese Alloy and Magnesium-zinc-zirconium Alloy

The most widely used magnesium alloys in the industrial market are Mg-Al alloys, followed by magnesium-manganese alloys and magnesium-zinc-zirconium alloys.

1. Magnesium-manganese alloy

Magnesium-manganese wrought magnesium alloy is a wrought magnesium alloy with magnesium as the matrix element and manganese as the first alloying element. Manganese can improve the stress corrosion cracking resistance of magnesium alloys, and has little effect on the strength, but reduces the plasticity of the alloy. According to the Mg-Mn binary phase diagram, there is a peritectic reaction at 623 °C: L+d-Mn→a-Mg. The maximum solid solubility of Mn in magnesium at this temperature is 2.2%; and then decreases as the temperature decreases, reaching 0.75% at 500°C and 0.25% at 400°C. Since magnesium and manganese do not form a compound, it is not a compound but pure manganese that is precipitated from the supersaturated solid solution, so the strengthening effect is small.

The casting properties of magnesium-manganese alloys are very poor, the solidification shrinkage is large, and the hot cracking tendency is large. The strength of the alloy is relatively large, and the improvement of strength properties mainly comes from work hardening. Therefore, almost all magnesium-manganese alloys in China are used in products processed by processing pressure. The magnesium-manganese alloy has a good extrusion effect, and the strength properties of extruded material are higher than that of rolled material. Manganese in the alloy can hinder the growth of grains during heating, so the decrease in strength properties after hot working and annealing is small.

Adding 0.15%~0.35% Ce to the magnesium-manganese alloy can further refine its grains and improve the mechanical properties of the alloy. The solubility of Ce in magnesium is very low, only 0.85% at 593 °C, and the solubility decreases with the temperature. It is reduced to generate Mg12Ce with high hardness and certain heat resistance, which improves the heat resistance of the alloy.

The main advantage of magnesium-manganese alloys is that they have both high corrosion resistance and good weldability. Mn is easy to combine with iron to form compounds, thereby weakening the adverse effect of iron on the corrosion resistance of the alloy and making the alloy corrode. The speed, especially in seawater, is greatly reduced. When the manganese content in the magnesium alloy is close to 1.5%, its corrosion rate in seawater is reduced to the lowest level, so the manganese content in the magnesium-manganese alloy is generally controlled at 1.3% ~ 2.5%. Mg-Mn alloys do not tend to stress corrosion cracking in neutral media, nor does intergranular corrosion occur.

Wrought magnesium-manganese alloys can be processed into various semi-finished products (plates, strips, tubes, bars, profiles, and forgings), plates are used to make aircraft, helicopter skins, panels, and internal components, forgings are used to make stressed parts, pipes It is mostly used in pipeline systems such as gasoline and lubricating oil that require corrosion resistance.

The processing of Mg-Mn alloy materials has no obvious effect on tensile strength, yield strength, and fatigue properties, but has a certain effect on elongation, fracture toughness, and impact toughness, which increases with the increase of manganese content. The magnesium-manganese alloy containing 1.5% Mn has the strongest corrosion resistance and increasing the manganese content not only decreases the plasticity but also decreases the corrosion resistance.

The alloy group of Mg-Mn alloy is MgMn, the grades are M1A, M1C, M2M, M2S, and ME20M, the mechanical properties are not too high, and the strength limit is 210-280MPa.

2. Mg-Zn-Zr alloy

Magnesium alloys are widely used in Mg-Zn-Zr alloys, which are magnesium alloys with magnesium as the matrix element, zinc as the first alloying element, and zirconium as the alloying element. In wrought magnesium alloys, Mg-Zn alloys are widely used, showing excellent aging strengthening behavior during heat treatment. In Mg-Zn binary alloys, zinc plays a solid solution strengthening the role and forming a strengthening phase, but Zn Increased hot cracking tendency and microporosity, inherent brittleness, and heat shrinkage. Zn is the first major alloying element. With the increase of Zn content, the solidification temperature range of the alloy becomes wider, the hot cracking tendency increases, and the weldability becomes worse. It cannot be used for casting complex shapes and manufacturing welded structures.

Zirconium can refine the structure, slow down the diffusion rate of the alloy, and prevent grain growth. It is an extremely effective grain refining element for as-cast Mg-Zn alloys, so it becomes a rare auxiliary alloying element for other magnesium alloys, forming a class of very practical zirconium-containing magnesium alloys such as Mg-Zn- Zr-based alloys and Mg-RE-Zr base alloys. Almost all Mg-Zn alloys contain 0.3% Zr to 1.0% Zr, and Mg-Re, Mg-Th, and Mg-Ag alloys all contain roughly the same amount of zirconium.

Mg-Zn-Zr alloys have good casting properties, hot working properties, and corrosion resistance, but the production process is complicated and the segregation tendency is large.

Adding rare earth elements to Mg-Zn-Zr alloys can form rare-earth-containing compounds at the grain boundaries during the solidification process of the alloys, which can improve the alloys’ casting properties and the structure of the castings.

In GB/T19078-2003, ZK series alloys are mainly Mg-Zn-Zr series magnesium alloys, which are also one of the most widely used wrought magnesium alloys, represented by ZK61 magnesium alloys. The tensile strength is greater than 300 MPa, with good plasticity and corrosion resistance, good machinability, and large forgings with complex shapes can be manufactured.

In GB/T19078-2003, cast magnesium-zinc-zirconium alloys include ZK51A and ZK61A alloys, and wrought magnesium-zinc-zirconium alloys include ZK61M and ZK61S. According to ASTM standards, Mg-Zn-Zr alloys mainly include ZK21A, ZK31, ZK40A, ZK60A, ZK51A, and ZK61M magnesium alloys.

Casting magnesium-zinc-zirconium alloys are mainly used for high-strength and impact-loaded parts in the aviation industry, such as aircraft hubs, rims, brackets, and parts with high working temperatures in the aviation industry; such as engine seats, motors shell, etc. Wrought magnesium-zinc-zirconium alloys are used for extruded products and die forgings with high strength and ductility.