Alloy Chemistry Behind the Two Flat Bars
2024 aluminum flat bar is an aluminium-copper-magnesium-manganese alloy. Copper and magnesium form the strengthening precipitates that respond to solution heat treatment and ageing, while manganese refines the grain structure and limits recrystallisation during hot working. The combination delivers high strength, strong fatigue resistance and excellent machinability without the brittleness of the very highest-strength grades.
7075 aluminum flat bar is an aluminium-zinc-magnesium-copper alloy. Zinc together with magnesium creates a denser and more effective precipitate network, which is why 7075 reaches the highest tensile and yield strength of any common wrought aluminium alloy. The trade-off is lower elongation, poor weldability and greater sensitivity to stress corrosion cracking unless the material is used in an overaged temper or given a protective finish.
Mechanical and Physical Properties Compared
The table lists typical room-temperature values for the two alloys in their most widely used tempers. Properties are direction dependent in rolled and extruded bar, so transverse values may be lower than the longitudinal figures quoted here.
| Property | 2024 Aluminum Flat Bar | 7075 Aluminum Flat Bar |
|---|---|---|
| Main alloying elements | Al-Cu-Mg-Mn | Al-Zn-Mg-Cu |
| Tensile strength | 450-483 MPa | 538-560 MPa |
| Yield strength, 0.2% offset | 324-345 MPa | 483-503 MPa |
| Brinell hardness | about 120 HB | about 150 HB |
| Shear strength | about 276 MPa | about 330 MPa |
| Elongation at break | 12-20% | 7-10% |
| Thermal conductivity | about 120 W/m.K | about 130 W/m.K |
| Weldability | Fair, requires a controlled procedure | Poor, prone to cracking |
Tensile testing is normally carried out to ASTM E8/E8M. Bar and extruded stock are commonly supplied to ASTM B211 or ASTM B221, while EN 755-2 is used for extruded bar in metric markets.
Machinability and Forming
2024 flat bar machines exceptionally well. Chips break cleanly, surface finish is easy to control and the alloy holds tight tolerances during CNC milling, turning and drilling, so it is the default choice for complex machined parts. It also forms reasonably well in the T4 temper, although tight bend radii are best formed before final ageing to avoid surface cracking.
7075 flat bar machines to an average level. Its higher hardness accelerates tool wear, so carbide or coated tooling, reduced cutting speeds and generous coolant are needed to avoid chatter and local work hardening. Forming is limited: bend radii must be large relative to thickness, and the material is usually machined to final shape rather than formed.
Corrosion Resistance and Surface Treatment
2024 flat bar offers good general corrosion resistance. Its copper content makes it less resistant than pure aluminium grades, and performance improves markedly with anodising, chemical conversion coating or a paint system. In chloride-rich service, machined edges benefit from complete coating coverage.
7075 flat bar has lower corrosion resistance and is notably susceptible to stress corrosion cracking when loaded continuously in the T6 temper. Anodising or conversion coating is standard practice for exposed service, and the T73 or T76 tempers are selected where sustained tensile stress and moisture occur together.
Cost, Typical Applications and Grade Selection
2024 flat bar costs less per kilogram and is stocked more widely in standard bar thicknesses, which makes it economical for high-volume machined components. 7075 flat bar carries a higher price because of tighter process control and more demanding heat treatment.
2024 flat bar: aircraft structures and fittings, automotive suspension and chassis parts, hydraulic manifolds, precision jigs and fixtures, gears and shafts.
7075 flat bar: racing chassis and suspension, military hardware, high-load aerospace fittings, injection mould tooling, load-bearing hardware.
Choose 2024 flat bar when the design needs an efficient balance of strength, fatigue life, machinability and cost, and when parts may need welding, bending or extensive machining. Choose 7075 flat bar when strength and stiffness govern the design, the geometry is machined rather than formed, and joints are made with mechanical fasteners instead of welds.
Confirm the temper as well as the alloy for critical parts. 2024 is usually supplied in T351 or T4 for forming and machining before ageing, while 7075 is generally supplied in T6, T651, T73 or T76 depending on the stress corrosion requirement.
Frequently Asked Questions
Q: Can 2024 aluminum flat bar be bent?
Yes. The T4 and T351 tempers have good formability and can be bent on a suitable radius, particularly when the bend is made before final ageing. Using a generous radius relative to thickness reduces the risk of surface cracking.
Q: Why is 7075 aluminum flat bar harder to weld?
Its high zinc and copper content promotes hot cracking and a loss of strength in the weld zone. Welded joints rarely recover parent-metal properties, so mechanical fastening, adhesive bonding or a different alloy is normally preferred.
Q: Which grade is better for CNC machining?
2024 flat bar is the better choice when production speed and surface finish matter, because it produces shorter chips and needs lower cutting forces. 7075 can be machined accurately but requires slower parameters and higher-performance tooling.
Q: How do T351, T4 and T6 tempers differ?
T351 is solution treated, stress relieved by stretching and naturally aged, giving stable dimensions for machining. T4 is solution treated and naturally aged with higher formability, while T6 is artificially aged to peak strength with lower ductility.
Q: Is 7075 always stronger than 2024?
In comparable tempers, yes: 7075 offers higher tensile and yield strength. However, 2024 retains more elongation and better fatigue performance in some loading conditions, so the stronger alloy is not automatically the better engineering choice.
Q: Which tempers and sizes are available?
Flat bar is produced in T351 and T4 for 2024 and in T651, T73 and T76 for 7075, in a wide range of thicknesses and widths. Cut-to-length supply helps keep material waste low on production runs.
