01-23-2018, 09:46 AM
When I weld aluminum plate 3/16" to 1/4" for truck bodies it loses its stiffness. The same thing happens when making panels for car bodies. If I heat the panels to about 400 or 500 degrees and let it cool, it becomes very flexible and I can form the plates very easily. How can I put the stiffness back into the plates after I am done forming it?
A - Aluminum alloys are normally purchased in a specific temper. In the case of the non-heat treatable alloys, this is the -H Temper, which relates to the strain-hardened condition of the material. In the case of the heat treatable alloys, this is the -T Temper, which reflects the thermal treatment that the material has been subjected to during manufacturing. Both of these temper methods are used to impart strength to the base material. The strengthening characteristics of the -H and -T Tempers can be significantly affected by heating of the base material.
After arc welding for instance, a reduction in strength is seen as well as an increase in ductility within a localized area adjacent to the weld. This area has been heated, during the welding operation, to a sufficient temperature for an adequate amount of time to anneal or partially anneal the base material. The same effect will occur when heating an entire panel. The heating operation will start to remove some of the strengthening that was introduced by the tempering operations and it will lower the tensile strength and increase the materials ductility (formability). The higher the temperature and the longer the time at temperature, the more pronounced the effect on the material.
Unfortunately, there is not a practical way to reintroduce the stiffness into the base material of a fabricated part after it has been reduced by heating. In theory, strengthening the effected material by strain-hardening or heat treatment could be done, however, because of the procedures required to perform these operations, it is not usually an appropriate option. Strain-hardening is achieved through controlled physical deformation of the base material, which generally involves a reduction in the cross-sectional area. Heat treatment to improve mechanical properties generally involves heating to a very high temperature followed by quenching in water and then controlled reheating for a further period of time. Post weld heat treatment of aluminum alloys is used in some specialized applications, however, there are a number of major considerations such as distortion of the fabricated part as it is heated and cooled through a very wide range of temperatures, practicality of physically heating and cooling the entire component and the cost involved with this elaborate procedure.
A - Aluminum alloys are normally purchased in a specific temper. In the case of the non-heat treatable alloys, this is the -H Temper, which relates to the strain-hardened condition of the material. In the case of the heat treatable alloys, this is the -T Temper, which reflects the thermal treatment that the material has been subjected to during manufacturing. Both of these temper methods are used to impart strength to the base material. The strengthening characteristics of the -H and -T Tempers can be significantly affected by heating of the base material.
After arc welding for instance, a reduction in strength is seen as well as an increase in ductility within a localized area adjacent to the weld. This area has been heated, during the welding operation, to a sufficient temperature for an adequate amount of time to anneal or partially anneal the base material. The same effect will occur when heating an entire panel. The heating operation will start to remove some of the strengthening that was introduced by the tempering operations and it will lower the tensile strength and increase the materials ductility (formability). The higher the temperature and the longer the time at temperature, the more pronounced the effect on the material.
Unfortunately, there is not a practical way to reintroduce the stiffness into the base material of a fabricated part after it has been reduced by heating. In theory, strengthening the effected material by strain-hardening or heat treatment could be done, however, because of the procedures required to perform these operations, it is not usually an appropriate option. Strain-hardening is achieved through controlled physical deformation of the base material, which generally involves a reduction in the cross-sectional area. Heat treatment to improve mechanical properties generally involves heating to a very high temperature followed by quenching in water and then controlled reheating for a further period of time. Post weld heat treatment of aluminum alloys is used in some specialized applications, however, there are a number of major considerations such as distortion of the fabricated part as it is heated and cooled through a very wide range of temperatures, practicality of physically heating and cooling the entire component and the cost involved with this elaborate procedure.