Welding?
You can weld the frame and it does not necessarily need to be heat treated. Not all aluminum's can be heat treated. The following was cut and pasted from an article on this topic and it explains it better than i can. Take the time to read it and know what material your frame is made of and you can make an informed decision yourself.
The non-heat-treatable alloys are composed of the 1XXX, 3XXX, 4XXX, and 5XXX series. It is not possible to strengthen these alloys by heat treatment. They can only be strengthened by cold working (also called strain hardening). The 1XXX alloys, such as 1100, 1188, or 1350, are essentially pure aluminum (99+% purity). They are relatively soft and weak, with good corrosion resistance, and are usually used where high electrical conductivity is required, such as for bus bars or as electrical conductors. They are also used in certain applications that require a high degree of resistance to corrosion. All of these alloys are readily weldable.
The 3XXX series of alloys have various levels of manganese (Mn) added to strengthen them and improve their response to cold work. They are of moderate strength, have good corrosion resistance, and are readily weldable. They are used for air conditioning and refrigeration systems, non-structural building trim, and other applications.
The 4XXX series of alloys have silicon (Si) added as an alloying element to reduce the melting point and increase their fluidity in the molten state. These alloys are used for welding and brazing filler materials and for sand and die castings. They are the least crack-sensitive of all the aluminum alloys.
The 5XXX series of alloys have magnesium (Mg) added in order to increase their strength and ability to work-harden. They are generally very corrosion resistant and have the highest strengths of any of the non-heat-treatable alloys. Increasing magnesium content in these alloys results in increasing strength levels. These alloys are commonly available in the form of sheet, plate and strip, and are the most common structural aluminum alloys. They are generally not available as extruded sections, because they are expensive to extrude. They are readily weldable, in most cases, with or without filler metal. However, there is an Al-Mg cracking peak at approximately 2.5% Mg, so care must be used in welding alloys such as 5052. It should not be welded autogenously (i.e., without adding filler metal). Weld filler metal with a high Mg content, such as 5356, should be used to reduce the crack sensitivity.
The heat-treatable alloys are contained in the 2XXX, 6XXX, and 7XXX alloy families. The 2XXX family of alloys are high strength Al-Cu alloys used mainly for aerospace applications. In some environments, they can exhibit poor corrosion resistance. In general, most alloys in this series are considered non-weldable. A prime example of a non-weldable alloy in this series, which is attractive to designers because of its high strength, is alloy 2024. This alloy is commonly used in airframes, where it is almost always riveted. It is extremely crack-sensitive and almost impossible to weld successfully using standard techniques.
Only two common structural alloys in the 2XXX series are weldable: 2219 and 2519. Alloy 2219 is very easily weldable and has been extensively welded in fabricating the external tanks for the U.S. space shuttle. This alloy gets its good weldability because of its higher copper content, approximately 6%. A closely related alloy, which is also very weldable, is 2519. It was developed for fabrication of armored vehicles. Although there are detailed exceptions to this rule, the designer should probably consider all other alloys in the 2XXX series to be non-weldable.
The 6XXX series of alloys are the alloys probably most often encountered in structural work. They are relatively strong (although not as strong as the 2XXX or 7XXX series) and have good corrosion resistance. They are most often supplied as extrusions. In fact, if the designer specifies an extrusion, it will almost certainly be supplied as a 6XXX alloy. 6XXX alloys may also be supplied as sheet, plate and bar, and are the most common heat treatable structural alloys. Although all alloys in this series tend to be crack-sensitive, they are all considered weldable and are, in fact, welded every day. However, the correct weld filler metal must be used to eliminate cracking. Additionally, these alloys will usually crack if they are welded either without, or with insufficient, filler metal additions.
The 7XXX alloys are the ones that usually trip designers up. They are the very high strength Al-Zn or Al-Zn-Mg-Cu alloys that are often used in aerospace fabrication, and are supplied in the form of sheet, plate, forgings, and bar, as well as extrusions. With the few exceptions noted below, the designer should assume that the 7XXX alloys are non-weldable. The most common of these alloys is 7075, which should never be welded for structural applications. In addition, these alloys often suffer from poor corrosion performance in many environments.
A few of the 7XXX series defy the general rule and are weldable. These are alloys 7003 and 7005, which are often seen as extrusions, and 7039, which is most often seen as sheet or plate. Some common uses of these alloys today are bicycle frames and baseball bats, both of which are welded. These alloys are easily welded and can sometimes offer strength advantages in the as-welded condition over the 6XXX and 5XXX alloys.
There is one other exception to the general rule that 2XXX and 7XXX alloys are unweldable. There are a number of thick cast and/or wrought plate alloys designed as mold plate material for the injection molding industry. These alloys, which include Alca Plus, Alca Max, and QC-7, are all very close in chemistry to 7075 or 2618. The designer should absolutely avoid structural welds on these alloys. However, welding is often performed on these alloys to correct machining mistakes, die erosion, etc. This is acceptable because there are only low stresses on such welds and, in fact, the weld is often in compression.
