The ageing process for extruded aluminum profiles
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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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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

  • The precipitation process is quite complex and involves the solubility of inter-metallic clusters that precipitate within the alloy


The Ageing Process

  • Natural ageing occurs with time, but requires too much time and floor space in the plant


The Ageing Process

  • Natural Ageing


The Ageing Process

  • Plants use artificial ageing in ovens to achieve maximum properties with efficient use of time and floor space


The Ageing Process

  • Artificial Ageing


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.


The Ageing Process

  • Most important to uniform ageing is how the oven is loaded.

  • Following are examples of incorrect loading practices:


The Ageing Process

  • Loading the Oven


The Ageing Process

  • Loading the Oven


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


The Ageing Process

  • Loading the Oven


The Ageing Process

  • Loading the Oven


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


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


The Ageing Process

  • Surveying The Oven


The Ageing Process

  • What oven design is best?

  • Most age ovens in North America are end-flow type


The Ageing Process

  • End-Flow Ovens


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


The Ageing Process

  • Cross-Flow Oven


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


The Ageing Process

  • Oven Loading: Cross-Flow or End-Flow?


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?


The Ageing Process

  • Quality control for ageing


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


The Ageing Process


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


The Ageing Process

¿Preguntas?

Al Kennedy

www.alkennedy.net

www.pressmaintmanual.com

alkennedy@usa.net


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