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

Transcription

1 for Extruded Aluminum Profiles By Al Kennedy Kennedy Eurotech Inc.

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

4 Natural Ageing

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

6 Artificial Ageing

7 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 185 o C (365 o F) for 4 to 5 hours. Most problems that occur are caused by non-uniformity of temperatures throughout the oven and throughout the load.

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

9 Loading the Oven

10 Loading the Oven

11 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 Loading the Oven

13 Loading the Oven

14 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 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 Surveying The Oven

17 What oven design is best? Most age ovens in North America are endflow type

18 End-Flow Ovens

19 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 Cross-Flow Oven

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

23 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 Quality control for ageing

25 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

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

28 Preguntas? Al Kennedy