Temper is a measure of a metal’s resistance to bending or kinking. In this post we look at the difference between T6 and T651. These tempers are bestowed by heating, quenching and cooling in a controlled way.
At Isizwe Metals we only stock T651.
There is no real difference in the mechanical properties of T6 and T651. The tempers, alloy composition and most metallurgical properties are similar. Both tempers have identical corrosion performance. The difference between the two is in the method of manufacture. The method has an effect on performance in certain applications.
T6 temper requires only solution heat treatment followed by artificial ageing. T651 is also heat treated and aged. But between the treatments the plate is stretched to flatten and relieve stresses. A plate gets quenched in water coolant after heat treating it. This is a complex process that leads to a high level of stresses induced into the plate. The process can distort the plate and create uneven flatness. In the case of the T651, the plate is stretched in a separate operation before ageing. The stretching removes all the quenched in stresses.
When the T651 plate gets machined it exhibits “post-machining stability”. It will not distort or buckle like the T6 as metal gets removed or the shape changed.
The T6 plate is not required to be stretcher levelled. And most often a roller levelling technique gets used to achieve an acceptable flatness. This process is much cheaper than stretching the plate. But does not relieve the quenching stresses. What it comes down to is the T6 plate’s temper can distort when the plate gets machined or cut. T651 is a safer general option.