Rare earth applications in nonferrous metals

1.Rare Earth Aluminum Alloy
In rare earth aluminium alloy research began in the 1930 s, during the second world war has been applied in the casting aluminum alloy, rare earth purpose is to improve the casting aluminum alloy of high temperature properties and casting properties. In the 20 years since the 1950s, there has been a great deal of work on the strengthening, deterioration, purification and improvement of rare earth elements in aluminum alloys. To date, progress has been made in the following areas.

(1) Reinforcement
Ceralumin with 0.15wt% Ce was first applied to high temperature working parts of engine cylinder body. Subsequently found, with 11 wt % on the strength of the alloy at 427 ℃ of rare earth can improve the 1 times. The former Soviet union has been applied in the supersonic aircraft containing rare earth А Ц Р 1 and Ж П 207 alloy, it is nowadays one of the best alloy high temperature performance, can be in long-term work under 400 ℃, its lasting strength aluminum alloy can be improved 1 ~ 2 times than normal. In addition, the development of Al - Cu - RE is a high strength heat resistant casting aluminum alloy, for example, aluminum alloy, containing 2 wt % RE at 300 ℃ of tensile strength of 160 mpa, room temperature strength of 350 mpa.

In the early stage, the strength and hardness of al-cu, al-cu -Si alloy piston can be improved by adding 0.3 ~ 0.35wt% Ce, and the heat crack can be reduced. Now, rare earth aluminum silicon eutectic and eutectic pistons have been used for production, and replacing nickel with rare earth can improve the high temperature performance and wear resistance of pistons, thus improving its life span.

The solubility of rare earth in solid aluminum is very small (< 0.05wt %), so its solid solution enhancement is very weak. But because of the rare earth chemical active sex is strong, it can form intermetallic compound with many elements in the alloy (AlCuCe, AlSiCe, etc.), they are very stable at high temperatures, high hardness and net-like distribution in grain boundary, can hinder the creep and slipping and moving, and thus have played an important role in high temperature reinforcement.

(2) Metamorphism
Rare earth of al-si eutectic and the bad behavior of hypoeutectic alloy, is to make the alpha + Si eutectic organization refinement, change from coarse silicon flake for thin strip and granule, which makes performance, especially the plastic. The metamorphism of lanthanum is the best, and the metamorphism of lanthanum can be further improved by increasing the magnesium content from 0.4wt% to 0.9wt %. Effective metamorphism of lanthanum range between 0.03 ~ 0.18 wt %, using rare earth as a modifier, speed corresponding demands some cold, the critical cooling rate of lanthanum m inimum value (Vc), when the Vc > 22 ℃ / min, can be effective. The metamorphism of rare earths also has long-term effects.

For example, the concentration of lanthanum is reduced from 0.056wt% to 0.035wt% after 10 remelting, and the content of this time is still in the best range of metamorphism.

(3) Purification
Rare earth has a strong affinity with h ydrogen, forming REH and so on, thus adding rare earth to the aluminum liquid can absorb some h ydrogen, thus reducing the pinhole caused by the precipitated h ydrogen in the solidification process. Addition of 0.2wt% RE, the hole rate can be significantly reduced.

In addition, the high magnesium content of aluminum alloy is easy to oxidize in liquid. In recent years found that when the Ce or RE contains 0.001 wt %, can be in 600 ~ 760 ℃ temperature block 10 ~ 12 wt % Mg alloy oxidation.

Adding rare earth impurities in still can make the aluminum alloy phase FeAl, AlFeSi form multiple metal compounds, which can change its shape, to improve the mechanical properties of aluminum alloy, such as in the alloy containing Fe 1 wt %, adding suitable amount of RE, can make the refinement and spheroidizing bulky iron phase.

(4) Improve process performance
Adding 0.2wt%Ce in the al-cu -Mn system can reduce the thermal crack tendency. A small amount of La, Ce and Y is added to the al-4wt %Cu alloy, which can reduce the solid phase line of the alloy and effectively reduce the heat vulnerable zone. Lanthanum can obviously improve the strength of the alloy quasi-solid. In addition, rare earth elements are concentrated in dendrites, resulting in the formation of metal intermetallic compounds such as LaAl and La (CuAl), reinforcing the grain boundary, thus reducing the tendency of thermal cracking.

In addition, still can change the aluminum alloy surface rare earth oxide film in the structure and properties of Al - Mg, Al - zinc - Mg alloy has better performance of colouring anodized, such as < 0.5 wt % Ce (or rare earth element) Al - zinc - Mg alloy is suitable for surface coloring of anodized materials. The rare earth also improved the corrosion resistance of al-si-mg alloy and added 0.15 ~ 0.2wt% La, which can improve the performance of the resistance to seawater corrosion.

2 Casting Copper Alloy
(1) Improve performance
In lead bronze, add 0.02 ~ 0.2wt% mixed rare earth, the grain size decreases (1/3 less than the original), and the surface wear decreases by 3/4. In the non-nickel high manganese aluminum bronze, adding a small amount of rare earth and boron can reduce the wear amount by 50%. In lead bronze, 0.05 ~ 1.0wt% mixed rare earth was added, the tensile strength increased by 30%, and the elongation rate was doubled. In aluminum bronze, 0.045wt% rare earth was added, and the elongation rate increased by three times when the tensile strength was not reduced.

Copper lead alloy with 0.055 ~ 0.2 wt % S, crystal phase in the alloy reticular tissue, add 0.028 ~ 0.149 wt % of rare earths, the crystal phase distribution between the dendrite in isolation, with the increase of sulfur content, fatigue strength decreases significantly; However, as the amount of rare earth increased, the fatigue strength increased significantly.

(2) Improve process performance

The rich lead of low melting point in lead bronze is easy to form inverse segregation. The more lead, the more serious the segregation. Add 1wt%Ce to eliminate segregation.

Silicon bronze was added 0.01 ~ 0.05wt% mixed rare earth, and the segregation of silicon and tin was improved.
In the Ce-8wt%Sn alloy, the addition of cerium can increase the effective distribution coefficient of tin and make grain refinement, thus inhibiting the formation of segregation.

The addition of 0.028wt%Ce in high manganese aluminum bronze, and 0.1wt% mixed rare earth in tin phosphor bronze, can obviously increase the fluidity, which can increase by 30% ~ 40%.

Cast magnesium alloy
Due to the emergence of rare earth (including thorium) magnesium alloy, the application of magnesium alloy has been developing rapidly since the 1950s. The role of rare earth in magnesium alloys can be summarized as: improving the resistance to creep, improving temperature and high temperature strength and improving process performance. As a result, the world's rare earth magnesium alloys now account for more than 50% of the cast magnesium alloy.

(1) High temperature resistant to creep alloy
First applied in aeroengine is Mg - RE - Zr (Mg - 3 RE - 0.1 - Zr) alloys, met the 205 ℃ has high strength and creep resistance.

(2) High intensity rare earth mg-zn -Zr alloy
ZK51 (Mg -4.5Zn-0.6 Zr) has the tensile strength of 280MPa, but poor casting performance. After the addition of rare earth, the Mg- zn-re compound was presented in the casting tissue, which was distributed in the grain boundary to improve the casting process performance.

ZE63A (Zn -6wt %, RE-2.5wt %, zr-0.6 wt %) has been used for years of thrust commutator of RB211 engine. Its tensile strength can reach 276MPa. Yield strength of 186MPa; The elongation rate is up to 5%.

(3) Contain yttrium rare earth magnesium alloy
Yttrium has a good strengthening effect on magnesium alloy, which is caused by the sealing of yttrium solids in the matrix and the heat resistant compounds in the grain boundary. Therefore, the y-mg alloy has high thermal performance and even the high temperature performance of thorium magnesium alloy. In addition, it has excellent high temperature oxidation resistance. Magnesium alloys containing 9 wt % in the moist air heated to 510 ℃, 98 hours only weight 1 mg; The magnesium alloys containing thorium gain up to 15mg.

Development and application of rare earth in non-ferrous metals in China although had began in the late 1960 s, but it was not until the national rare earth non-ferrous application network, established in 1985, after the organization promoting rare earth application in aluminium wire and cable have breakthrough, consumption increases year by year. In 1985, it was 330 tons of REO. In 1994, it was 600 tons of REO. In 2003, it was 1000 tons of REO, with an average annual growth rate of more than 13%. In addition to aluminum alloy, the application is successfully used in copper alloy, hot-dip galvanized alloy, hard alloy and magnesium alloy. At present, the development and application of rare earth in non-ferrous metals and alloys have been proved to be effective in aluminum, copper, magnesium, titanium, molybdenum, nickel, cobalt, niobium and platinum metals.

The addition of rare earth metals in these nonferrous metals and alloys is generally less than 0.5%, but the effect is remarkable. Rare earth can be used to purify, deteriorate and refine grain. , in particular, by adding rare earth aluminium wire, cable, eliminates the negative impact of the silicon and the conductive performance not only slightly higher than the international electrotechnical commission standards, and the strength increased by 20%, the corrosion resistance increased by more than 1 times, wear-resisting performance improved 10 times, every change the backwardness of the aluminum wire and cable industry in China, the rare earth aluminum wire and cable products has become a national power grid of the regulation, annual production capacity of 450000 tons, and has entered the international market, the technology has aroused abroad attention.

These aluminum wires and cables are put into use and can save $4 billion a year for the state, with a benefit of 2 billion yuan. The annual output of aluminum alloy and cast aluminum alloy can reach 33-340,000 tons, the annual output of rare earth copper and brass can reach 60,000 tons, and the production of rare earth hot galvanizing products can reach 30,000 tons. The amount of rare earth in nonferrous metals is increasing year by year. The consumption of rare earth metals in nonferrous metals in 1990 ~ 2003 is shown in table 1.