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The Ageing Process for Extruded Aluminum Profiles

The Ageing Process for Extruded Aluminum Profiles. By Al Kennedy Kennedy Eurotech Inc. The Ageing Process. Extrusions in Al-Mg-Si family are aged to improve properties Called “age hardening” but goal is not hardness, but increased ultimate tensile strength and yield strength

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The Ageing Process for Extruded Aluminum Profiles

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  1. The Ageing Process for Extruded Aluminum Profiles By Al Kennedy Kennedy Eurotech Inc.

  2. The Ageing Process • Extrusions in Al-Mg-Si family are aged to improve properties • Called “age hardening” but goal is not hardness, but increased ultimate tensile strength and yield strength • The precipitation process is quite complex and involves the solubility of inter-metallic clusters that precipitate within the alloy

  3. The Ageing Process • Natural ageing occurs with time, but requires too much time and floor space in the plant

  4. The Ageing Process • Natural Ageing

  5. The Ageing Process • Plants use artificial ageing in ovens to achieve maximum properties with efficient use of time and floor space

  6. The Ageing Process • Artificial Ageing

  7. The Ageing Process • These charts from the paper Precipitation Aging by R.W. Hains show that maximum properties are achieved quickly under controlled temperatures and time. • From these and similar references the ideal process parameters of time and temperature can be defined for ageing profiles of different alloys. • A common process for ageing alloy 6063 is at 185oC (365oF) for 4 to 5 hours. • Most problems that occur are caused by non-uniformity of temperatures throughout the oven and throughout the load.

  8. The Ageing Process • Most important to uniform ageing is how the oven is loaded. • Following are examples of incorrect loading practices:

  9. The Ageing Process • Loading the Oven

  10. The Ageing Process • Loading the Oven

  11. The Ageing Process • Most important principle: hot air must pass through the load, with maximum contact with the extrusions • If hot air can by-pass the load, over the top or around the sides, ageing will not be uniform and the heating cycle will be much longer

  12. The Ageing Process • Loading the Oven

  13. The Ageing Process • Loading the Oven

  14. The Ageing Process • The age cycle has two parts: • Heat-up, or time for the entire load to reach temperature, and • Time at correct temperature for ageing or precipitation • Must assure that the entire load is at the correct temperature for the specified time

  15. The Ageing Process • Conduct frequent surveys of oven temperature, to assure uniform temperatures • Locate thermocouples throughout the oven to check for hot and cold places • Make surveys every 3 months to 1 year

  16. The Ageing Process • Surveying The Oven

  17. The Ageing Process • What oven design is best? • Most age ovens in North America are end-flow type

  18. The Ageing Process • End-Flow Ovens

  19. The Ageing Process End-Flow Ovens Advantages: • better thermal efficiency • more open area within the load for air flow • not affected by short profile loads • Requires less floor space • Cheaper to build Disadvantages: • less temperature uniformity end-to-end

  20. The Ageing Process • Cross-Flow Oven

  21. The Ageing Process • Cross-Flow Ovens Advantages: • better temperature uniformity Disadvantages: • less thermal efficiency • less open area for air flow • adverse effect for short profile loads (air can by-pass the load) • More expensive and more floor space required

  22. The Ageing Process • Oven Loading: Cross-Flow or End-Flow?

  23. The Ageing Process Decision: Cross-Flow or End-Flow? Consider the mix of profiles to be aged: • how are they stacked? • Is there space between the layers? • what is the maximum open space for air flow? • does the length of loads allow by-passing? • can air by-passing be avoided?

  24. The Ageing Process • Quality control for ageing

  25. The Ageing Process • A study by Mr. Bob Werner was presented at ET 84 Seminar • He concluded that Webster hardness testing is not reliable enough for testing the properties of ageing. • He recommended full tensile and yield testing as first choice • Barcol is second choice • Rockwell E is the third choice

  26. The Ageing Process

  27. The Ageing Process • Ageing cycle is determined by alloy • Good properties require uniform temperatures and uniform time-at-temperature • Uniform temperature depends on how the oven is loaded • Prevent hot air from by-passing the load • Take temperature surveys to assure quality

  28. The Ageing Process ¿Preguntas? Al Kennedy www.alkennedy.net www.pressmaintmanual.com alkennedy@usa.net

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