BILBAINA DE TRATAMIENTOS
HARDEN THE ALUMIMIUM
Aluminum is a metal whose chemical symbol is Al, atomic number 13 , and its atomic weight is 26.9815 . Pure aluminum is soft and has little strength , but can form alloys with other elements to increase your stamina and acquire several useful properties.
Aluminum alloys are lightweight , strong , and easy training, are easy to assemble , cast or machined and accept a variety of finishes . By their physical properties , chemical and metallurgical , aluminum metal has become the most widely used non-ferrous .
According to types of treatment are used to harden the aluminum , they can be classified into two groups :
ALLOYS WITH NO temperable hardening
HARDENING WITH STRUCTURAL hardenable alloysStructural hardening alloys is that their mechanical characteristics depend tratamientostérmicos , solubilization , quenching and aging (natural or artificial ) . This group includes families 2000 (Aluminum -Copper ) , 6000 (Aluminium -Magnesium -Silicon ) and 7000 (Aluminium -Zinc ) .
The heat treatment for hardening of these alloys follows the following sequence :
1 – SOLUBILIZATION
At elevated temperature is of the order of 530 º C , this temperature is higher when the alloy is loaded with the alloying elements , magnesium, silicon and zinc. The temperature holding duration depends on the thickness of the products.
During prolonged maintenance at high temperatures, the intermetallic compounds of type Mg , Si, Cu, Zn, and the alloy redissolved then forms a homogeneous solid solution .
Start temperature solution of aluminum alloys structural hardening must be precisely regulated to avoid reaching the eutectic temperatures produce local melting of the intermetallic compounds . The metal is then unusable.
2 – TEMPLE
This is a very rapid cooling of the metal is normally by immersion in cold water at the outlet of the furnace. The brutal metal cooling has the effect of preventing the precipitation of intermetallic compounds .
It is immediately after quenching when precipitation hardening alloys ( AlCu – AIMgSi – AlZn ) are easily deformed . The quench rate is an important parameter which depend certain properties , such as tensile mechanical properties , toughness, corrosion resistance …. There for each alloy a critical speed of hardening under the sill is must come down.
The maximum tenacity for the quench rate must be three times faster than the critical quenching speed . Note: the tempera are capable of producing internal stresses particularly in complex parts or large sections.
Tension can be decreased with a controlled plastic deformation , for example, a 2% tensile elongation after quenching and before maturation natural good ( T451 ) or artificial ( T651 ) .
After tempering the supersaturated solid solution is in a metastable state . The return to equilibrium, ie precipitation of intermetallic compounds that cause structural hardening , it can be done in two ways :
– By maturation at room temperature ( natural aging ) . After standing several hours, depending on the alloy , the hardness and mechanical properties do not increase . Precipitation and structural hardening over. T4 is the state
– By tempering , ie heating of several hours between 160 and 180 degrees . Tempering ( artificial ripening ) accelerates precipitation. Was performed immediately after quenching . Annealing conditions depend on the alloys.