Aluminium alloy will change strength

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Discussion Overview

The discussion revolves around the strength changes of aluminum alloys when subjected to varying loads compared to static loads. Participants explore concepts related to cyclic loading, work hardening, and specific alloy properties, including yield and ultimate strengths.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether aluminum alloys change strength under varying loads, expressing uncertainty about the mechanisms involved.
  • Another participant suggests clarifying the question, indicating that it may relate to cyclic loads, S-N curves, or work hardening.
  • A participant suspects the discussion pertains to fatigue and references the Bauschinger Effect as relevant to the topic.
  • It is noted that several aluminum alloys are strengthened through work hardening, which may influence their response to loading conditions.
  • A participant poses two questions regarding the strongest aluminum alloy and whether its strength characteristics change under cyclic loading, suggesting AlCu4Mg2 as a candidate for the strongest alloy but expressing uncertainty.
  • Another participant mentions that 7001-T6 is known for its high tensile strength and provides specific values for tensile strength and endurance limit, emphasizing that cyclic loading effects depend on the load applied and can lead to strain hardening, increasing strength but also brittleness.

Areas of Agreement / Disagreement

Participants express differing views on the effects of cyclic versus static loading on aluminum alloys, with no consensus reached on the strongest alloy or the implications of loading conditions on strength characteristics.

Contextual Notes

The discussion includes assumptions about the definitions of cyclic loading and fatigue, as well as the specific properties of various aluminum alloys, which may not be fully resolved.

Who May Find This Useful

This discussion may be of interest to materials scientists, engineers working with aluminum alloys, and students studying material properties under different loading conditions.

TSN79
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Is it the case that an Aluminium alloy will change strength (yield/ultimate) if subjectet to a varying load instead of a static one? I can't quite see why it should...can someone help me with this?
 
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You need to phrase your question a bit better. Are you talking about cyclic loads past the elastic limit? Are you referring to an S-N curve issue? Or are you possible talking about work hardening?
 
I suspect it is the former.

(TSN, you could look up "fatigue" and its origin in the "Bauschinger Effect". )
 
On the other hand, several Al-alloys are strengthened by work hardening...
 
Well, I have two questions to answer. First, which Al alloy is the strongest, and in what region would the yield/ultimate strengths for this alloy lie?
Second, Is this region the same if the alloy is subjectet to cyclic loads instead of static loads?

On the first question I suspect the combination AlCu4Mg2 is the strongest, but I'm not at all sure...
 
There are so many different alloys of aluminum out there, this is a bit of a tough question to answer.

Of the basic alloys that I am familiar with, 7001-T6 has the highest tensile strength of approximately 97 ksi. 7001-T6 is a zinc-copper-magnesium alloy that is age hardened.

In terms of cyclic loading, this is where you will want to look up an S-N curve for that material. The endurance limit for this alloy is 21.8 ksi which, as shown is for 500x10^6 cycles (infinite life). To answer your question, it will depend on how much load you are cyclically placing on the material. If you are continuously cycling past the yield point, you will strain hardent the material. In that case it will become stronger, but also much more brittle and, obviously, the fatigue life drops.
 

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