Introduction to Copper alloys (brass, Bronze, copper)
The addition of zinc to copper increases the strength of the alloy and, at the same time, its plasticity, which is a very important function.
10-20% zinc alloy is called gold plating metal, used in jewellery and heat exchanger production; The 30% zinc alloy is called cartridge brass. The highest threshold for zinc in moulded brass is about 35%.
The addition of other alloying elements can further improve the performance of brass. Tin and aluminium, for example, improve their corrosion resistance in seawater.
Single phase brass
Applications: Jewelry, artwork, tableware, Musical Instruments and ammunition cartridges.
Single-phase brass, which contains up to 37% zinc and is known as alpha brass, has a uniform crystal structure and is softer and more malleable. These qualities make Alpha brass suitable for cold working, drawing, bending and other processes.
Application: Heat exchangers, capacitors, automatic cutting table parts, etc.
Biphasic brass contains both α and β phases, i.e. both α grain structure and β grain structure are present. Duplex brass is cheaper than single-phase brass because it uses a lot of zinc and is also prone to corrosion. Its chemical composition gives it greater strength and hardness and, therefore, is suitable for processes such as thermoforming and casting.
Bronze alloys are classified into different types according to the alloying elements used.
Application: spring, washers, coins, crafts, pump parts, pressure castings, bearings, etc.
Its application depends on the percentage of tin used in the alloy. The full tin content in alloys suitable for hard work is about 7%, and these copper alloys have good plasticity.
The maximum tin content is about 20%. Starting from 5% tin, the structure of the alloy changes and requires some additional heat treatment, which results in a porous structure, which is why they are not suitable for forming methods other than casting.
The main application of biphasic tin bronze is in the bearing industry. This structure has a good balance, where the α phase ensures resistance to hitting while the hard and brittle compound bears the load and provides some wear resistance.
Zinc and lead are sometimes present in tin bronze. Zinc improved the quality of the casting and also made the alloy cheaper. This Bronze was also known as gun copper because it was used to make large guns.
A small amount of lead helps to improve the mechanical cutting properties of Bronze. The lead Bronze used as a bearing material has a higher lead content (up to 25%).
Application: Coins, ship parts, hardware, sleeve bearings, pumps, valves, etc.
Aluminum-bronze has similar characteristics to tin bronze, is mostly single-phase and suitable for cold forming, and is very suitable for making coins, where the aluminum content is usually between 6 and 12%.
Duplex aluminum bronze can be used as a casting alloy or for hot working. Aluminum bronze, with an aluminum content of about 10%, is used to make propellers, valves, pumps, etc.
Application: Coin, Marine equipment, electrical equipment, heat exchanger, cooling system, shipbuilding, etc.
Copper-nickel alloys are strong and malleable. Adding nickel to copper (usually 2-30%) makes the metal highly resistant to corrosion and has excellent electrical conductivity.
Copper-nickel alloy at 40… Constantan (Cu-Ni alloy with 45% nickel) is used for electrical equipment with high-temperature variation because it has almost no thermal expansion coefficient and maximum resistance at 50% nickel.
The corrosion-resistant copper-nickel alloy contains about 30 per cent nickel and small amounts of iron and manganese, which are particularly stable in salt water.
The advantages of copper die casting.
Copper die casting is a kind of high-temperature die casting method in which liquid copper or copper alloy is filled into the cavity of die casting mold with high speed under high pressure, and copper or copper alloy is solidified under pressure to form casting. Advantages: High precision casting, can produce parts with complex structure, high production efficiency for mass production.
Copper alloy die-casting die material
With industrial pig iron as the main raw material and scrap steel, ferric molybdenum and ferric vanadium as additional raw materials, the copper alloy die-casting material was prepared by smelting in a 20 kg medium frequency induction heating furnace. The influence mechanism of yield strength, impact toughness and P element distribution on the properties of die-casting die materials was studied. The results show that the prepared copper alloy die-casting material has good yield strength and impact toughness with the addition of 0.6% Zn, which are 415MPa and 10.6 J·cm-2, respectively. Adding the proper amount of Zn element can significantly reduce the segregation of P element in the grain boundary of die casting die material, improve the impact toughness of die casting die material, and thus improve the resistance to thermal shock and thermal fatigue damage of die casting die steel.
What die steel is used for copper die casting
Now choose imported 8407 copper die casting mold, with a life of about 2000 die times. Previously used H13, 2344, SKD61, die life is hundreds of die, die is washed corrosion, began to crack. Tried a variety of die steel, but die life has been unstable.
The key factor for the short life of the copper die-casting mold and the easy erosion of the mold is the high melting temperature of the copper alloy, which is about 950℃. The vast majority of hot working die steel can not resist such a high temperature for a long time; the annealing temperature of die steel is about 600℃. When the copper dies casting mold is working, the die steel should come into contact, the high temperature and high-pressure liquid copper alloy is washed out, the temperature drops rapidly after demold, and the die steel frequently alternates between hot and cold. The hardness will decrease quickly if the die steel is not resistant to burning. Thus by high temperature and high-pressure copper alloy erosion, the formation of cracking. From cracking to cracking until the mold scrap.
The key to choosing to die steel for copper dies casting mold is to find die steel with fire resistance. At present, only 8433 die steel can be pushed. There is a copper die-casting product with a wall thickness of 20mm. When the imported 8407 is used for production, the mold begins to be eroded and corroded after its life of about 600 times, forming cracking. After 8433 is used, the life of the mold is increased to about 2000 molds, and the mold begins to be partially eroded and corroded, and it can continue to be used after mold repair. The price of 8,433 is 30% lower than that of the imported 8,407.
Factors of copper alloy die casting life
On the one hand, during the injection process, the die-casting mold is impacted by high speed and high-pressure injection of high-temperature liquid copper (the speed at the inner gate can reach 40 ~ 55 m/s, and the filling pressure is generally 40 ~ 80 MPa). The filling pressure and speed are very large, so the surface of the mold cavity is under great mechanical stress.
On the other hand, the temperature of liquid copper is high, and every time from the completion of injection to the re-injection, the die core works in the cyclic mode of “thermal expansion and cold contraction”. The cavity temperature of the mold repeatedly changes between 360℃ and 550℃. The mold is often cold and hot and is subjected to the action of compressive stress and tensile stress. Figuratively speaking, it is like pulling the rubber band repeatedly, and the rubber band surface will appear turtle crack until cracking.
Therefore, the main reason for mold damage is affected by cyclic mechanical stress and thermal stress, leading to cavity surface fatigue damage, the formation of turtle cracks, and even the overall cracking failure of the mold core. Therefore, die life extension should mainly reduce mechanical and thermal stress.
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