Introduction to 20-200 mm Aluminium Plate
Aluminium plate in the 20 mm to 200 mm thickness range is used for heavy-duty industrial equipment, structural components, marine fabrication, tooling, moulds, and transportation equipment where high strength and low weight must be combined. Unlike thin sheet, thick plate is usually supplied as flat-rolled or sawed product with defined flatness, edge condition, and internal quality requirements. The choice of alloy depends on the service environment, the loading, and the joining methods planned. Common grades are 6061, 5052, 5083, 5754, 7075, and 2024, and the applicable standards include ASTM B209, EN 485-2, and GB/T 3880.
Alloy and Temper Overview
6061-T651 offers a balanced combination of strength, machinability, and corrosion resistance, and is widely used for structural and machined parts; typical reference values are a tensile strength of about 290-340 MPa, a yield strength of about 240-310 MPa, and 8-12 percent elongation. 5052-H32/H34 provides good corrosion resistance and formability with tensile values around 210-280 MPa, suitable for marine and fabricated components. 5083-H116/H321 is an established marine alloy with high corrosion resistance and good weldability, typically 275-350 MPa tensile. 5754-H22/H32 offers good formability for transportation and architectural fabrication, around 190-260 MPa. 7075-T651 reaches very high strength, about 500-570 MPa tensile, for aerospace, tooling, and high-load components, and 2024-T351/T851 provides high strength with good fatigue performance but requires corrosion protection outdoors. These figures are representative reference ranges, not guaranteed values; the exact minimums must be taken from the material standard and mill certificate.
Corrosion and Environment Considerations
For coastal and humid environments, 5xxx-series alloys such as 5052, 5083, and 5754 are attractive because of their proven corrosion resistance, with 5083 particularly established for marine structures. Heat-treatable alloys such as 6061, 7075, and 2024 have good atmospheric performance but may require protective coating in aggressive or outdoor conditions, and 7075 and 2024 are more susceptible to stress-corrosion cracking in certain tempers and grain directions. When thick plates are used in seawater or industrial atmospheres, specify the appropriate temper, consider cladding or coating, and design joints to avoid crevices. Corrosion protection, fatigue design, and joining methods must be evaluated together rather than selecting an alloy on strength alone.
Welding and Joining of Thick Plate
Laser welding can produce a narrow heat-affected zone, low distortion, and high welding speeds with many aluminium alloys, particularly 5xxx-series and selected 6xxx-series materials, provided equipment, joint design, filler strategy, and parameters are properly controlled. 5083, 5052, and 5754 are generally suitable for welding because they are non-heat-treatable with good weldability; however, welding still affects local mechanical properties, residual stress, and corrosion performance. Surface preparation is essential because aluminium oxide melts at a much higher temperature than the base metal, so oil, moisture, dirt, and heavy oxide must be removed before welding. 6061-T651 can be laser welded, but the heat-affected zone loses part of the T651 strength, so joints must be evaluated for the structural load. 7075 and 2024 are more difficult to weld; their high strength and alloying content increase cracking risk, and fusion welding is generally avoided for critical applications unless a qualified procedure is developed. For plates in the 100-200 mm range, joint preparation, preheating where appropriate, shielding gas, filler selection, and distortion control require engineering validation.
Selection Guidance by Application
For general structural components, 6061-T651 provides a useful balance of strength, corrosion resistance, machinability, and cost. For coastal and humid environments, 5052, 5083, and 5754 are preferred for their corrosion resistance, with 5083-H116 or H321 the established choice for welded marine structures. For complex formed components, 5052 and 5754 offer better formability than high-strength heat-treatable alloys. For high-load aerospace and precision engineering, 7075 and 2024 provide substantially higher strength, but corrosion protection, fatigue design, and joining methods must be carefully considered. Specify the correct temper for heat-treatable alloys, such as T6, T651, T351, or T851, and the required H temper or O condition for 5xxx-series alloys.
Ordering and Quality Checklist
Before ordering 20-200 mm plate, confirm the alloy, temper, thickness, width, length, applicable standard, flatness, dimensional tolerances, non-destructive testing requirements such as ultrasonic inspection, and mechanical-property requirements. For aerospace, marine, or structural applications, request a mill test certificate and any required third-party inspection documentation. Store thick plates flat on suitable supports in a clean, dry, covered area, and protect surfaces from moisture, contamination, and mechanical damage. When higher strength than 6061 is needed, consider established grades such as 6082 under EN specifications, and verify the chosen alloy against the design requirements rather than relying on unverified commercial designations.
FAQ
Which alloy is best for marine structures in thick plate?
5083 in the H116 or H321 temper is the established choice for welded marine structures because of its combination of strength, weldability, and seawater corrosion resistance. 5052 and 5754 are also used in less demanding marine applications.
Can 7075 thick plate be welded?
7075 is difficult to weld because its high strength and alloying content increase the risk of cracking and local strength loss. Fusion welding is generally avoided for critical applications unless a qualified welding procedure is developed and tested.
Why does thick plate strength vary with thickness?
Mechanical properties are influenced by the degree of working, heat treatment response, and cooling rates, which change with section thickness. Larger thicknesses often have slightly lower strength and ductility than thin sections of the same temper, which is why minimum values are specified per thickness range.
What is the difference between T6 and T651 tempers?
T6 is solution heat treated and artificially aged. T651 includes an additional stress-relieving stretch after solution treatment, which reduces residual stress and improves flatness and machining stability, making it preferred for thick plate that will be machined.
Is laser welding suitable for 20-200 mm aluminium plate?
Laser welding can be used with proper joint design and process control, but thick sections require high-power equipment, careful parameter development, and often multiple passes. For plates above 100 mm, engineering validation of preheating, filler, shielding, and distortion control is essential.
Should I request ultrasonic testing for thick plate?
For aerospace, marine, and critical structural applications, ultrasonic or other non-destructive testing is commonly specified to verify internal soundness. Confirm the acceptance criteria with the applicable standard and state the requirement when ordering.