Alloy 6060 and alloys 6063 and AD31
Aluminium alloy 6060 It is the most popular aluminum profiles Extruders, bars and tubes. The nearest “relatives” alloy 6060 – Aluminium alloy 6063 and AD31.
Aluminium alloy 6060 – this is “diluted” alloy 6063: it has less magnesium and silicon. Aluminum alloys 6063 and AD31 are almost identical – the differences are only in the iron content and in the accuracy of chemical composition control (see. Comparison of Aluminum Alloys 6060, 6063 and AD31). therefore technological pressing box – optimum compaction paarametry – these alloys by the example alloy 6060. for alloys 6063 AD31 and differences will be minimal.
Heating of the workpiece for pressing
The purpose of heating the preform – lower alloy flow stress for pressing at maximum speed and to obtain a good surface and predetermined mechanical properties aluminum profiles.
The heating temperature should be sufficient to dissolve the particulate β'-Mg2Siv during pressing. This ensures the achievement of optimum mechanical properties of aluminum profiles with subsequent quenching on a press and artificial aging.
A typical heating temperature for low-alloyed alloys of the series, such as Alloy 6060, It is from 430 to 470 ° C depending on, how difficult it is to press Profile cross-section, alloy type, predetermined level of mechanical properties and surface quality of the finished aluminum profiles.
Apply two basic types of heating the preforms - in the gas tunnel furnaces and induction furnaces.
Induction heating of billets
In the latter case, heating occurs very quickly: the workpiece reaches the set temperature in a matter of minutes.. Such rapid heating gives much time to change the microstructure of a homogenized ingot. This may adversely affect the compressibility of the alloy, but it is useful for the mechanical properties of the profiles.
The homogenised microstructure comprises mainly relatively small particles β'-Mg2And, as well as magnesium and silicon in solid solution. Magnesium and silicon in solution, remaining in solution, will increase the voltage of the hot flow the preform and therefore to reduce the compression rate.
At the same time, rapid temperature rise after an interval of 200 to 450 ° C is a useful, as it excludes the formation of coarse particles of β-Mg2And. These coarse particles of β-Mg2Si do not have time to dissolve in the pressing and necessary to avoid their formation in order, to obtain optimum mechanical properties.
Gas heating workpieces
When the gas is heated the situation is almost the reverse. The slow rise in temperature allows homogenized microstructure change so, that magnesium and silicon may fall out of solution as a particulate β'-Mg2And. This reduces the flow stress of hot workpiece and allows higher press speed.
Negative gas heating factor is the possible decrease of the mechanical properties of the final. A slow or long heating to a temperature 400 ° C promotes coarsening of particles β'-Mg2And. At a temperature of about 400 ° C begin to form particles of β-Mg2And. β'-Mg Coarse2Si require for dissolving higher temperature at the outlet from the press, and particles β-Mg2Si do not have time to dissolve for pressing time. The reduced concentration of dissolved particles Mg2Si in solution will lead to, after artificial aging strength properties will be below the optimum.
Heating of the workpiece when stopping the press
For the same reasons, if the workpiece is kept at an elevated temperature for too long (for example,, due to the stop of the press) the microstructure of the workpiece is destroyed by the optimized homogenization and this leads to a reduced compressibility of the workpiece and low mechanical properties of the profiles after subsequent artificial aging.
Pressing of aluminum profiles
Aluminum profiles (and pipes) from 6xxx series alloys are pressed almost exclusively by direct pressing. In this method the blank, in the container, under the influence of hydraulic force is extruded (extruded) through one or more holes in a fixed matrix.
The preform is heated to a temperature of 450 to 500 ° C depending on the alloy, profile cross-sectional shapes and pressing ratios (drawings). The heated preform is charged into a container, warmed up 420 – 470 ° C. Hydraulic press ram retracts into the container under pressure and pushes the blank about 700 MPa through one or more openings matrix. The hot metal of the workpiece is pressed through the matrix and forms a long (meters up to 50) aluminum profile cross section, which is identical to the outlet of the matrix. Sometimes all that, that comes out of the matrix, called scientifically “extrudate”, and often – “whip” and several “weave”.
Technological pressing box
The maximum press force
The maximum press force sets the maximum possible pressing speed at a given billet temperature (Red line). This line shifts to the left when softer (less alloyed) alloys are used.. Harder alloys, a higher ratio of compression or a more complex cross-section aluminum profile shift the limit line to the right. Higher temperature preform can achieve higher compression rate, if it will allow other factors.
The surface quality of aluminum profiles
The blue line defines a boundary between "poor" and an acceptable surface quality of the pressed aluminum profile in the coordinates "preform temperature" and "compression rate". This boundary is shifted to the right in the application of "soft" alloys, which allow higher speed pressing and heating the preform until the temperature profiles unacceptable surface defects.
Sophisticated aluminum profiles, a high ratio of pressing and "hard" alloys shift the border left. Moreover, offset to the left reduces the likelihood of the profiles of surface defects as a teaser and adhered. To avoid these defects aluminum extrusions lower compression rate and the preform heating temperature. Coarse β-Mg2And, formed during slow cooling after homogenisation or too slow heating of the workpiece, also shifted the siniyu line to the left.
The mechanical properties of aluminum profiles
Requirements on the mechanical properties of the finished aluminum profiles also imposes some restrictions on the compression parameters. Green Line the boundary between “adequate” and “inadequate” mechanical properties. This line is shifted to the right while pressing the preform with coarse particles of β-Mg2And, pressing "thick" sections and then, when improved mechanical properties. In these cases, the requirements on the mechanical properties necessary to increase the compression rate and increase the temperature of the preform. can say, it gives admission to the procurement of additional energy, which is necessary to dissolve the coarse particles of β-Mg2And.
for blanks, in which the microstructure is dominated by particle β "-Mg2Siи β’-Mg2And, for thin-walled profiles and aluminum profiles without the requirements on the mechanical properties green Line moves to the left. This reduces restrictions on the compression rate and temperature of the billet, and the required mechanical properties of the aluminum profiles are easily achieved.