Guuuuyyyys...
I want to caution everyone there are numerous misconceptions and miss-statements throughout this post. A few guys have made corrective statements... but not enough. And this starts with skittish’s presentation as to what rivets he was dealing with... ‘17-T4 really hard to drive’ with a raised dot.... which were probably purchased at a ‘bargain price’ surplus sale@... since they are rarely used anymore... except in antique/heavy jet [707, 727, DC-8, etc] structural repairs. @ on-a-dare, I will even bet that the label on the bag holding the rivets... if legible... indicates date of manufacture +25-years-ago.
In this case I would normally advise installing ‘B’ or ‘A’... or maybe ‘AD’... and NEVER mess with any heat treatment. OH by-the-way... I can’t figure-out WHAT finish was applied to the original rivets... and that has a large effect on this situation also.
Applying heat to these rivets for any purpose is a really bad idea... and in the long term You will not be happy with the results... even for the ‘non-aviation’ purposes described... “soften them so they can be installed ‘safely’ in 5052-O or –H32[?] aluminum sheet, tubes, etc.
Heat treating aluminum alloy rivets is as critical as heat treating aluminum parts: knowledge and hands-on training is essential.
1. First, let’s consider as-manufactured alloys solid rivets you are likely to use [specifications listed]
NASM20426 100-degree flush tension head [MS20426, was AN426]
NASM20470 protruding tension head [MS20426, was AN470]
NAS1097 100-degree flush shear [reduced-height] head
Alloy-code... head symbol... Alloy-temper... Finish
A... [none]... 1100-as forged.. CCC$
AD... depressed dot [dimple]... 2117-T4... CCC$ or Anodize#
B... raised cross [+]... 5056-H32... CCC$ or Anodize#
D... raised dot [tit/teat]... 2017-T4... CCC$ or Anodize#
DD... raised dash-dash [- -]... 2024-T4... Anodize# [only]
E... indented ring [o]... 7050-T73... CCC$ or Anodize#
KE... raised ring [o]... 7050-T73... CCC$ or Anodize#
3. How they are made.
High quality aluminum alloy wire per specification ASTM B318 [was] QQ-A-430] is fed into the cold heading machine coated with lubricant and are then forged/cut/rolled to a few standard shank lengths... 'shaped-blanks' of semi-finished size/length. These blanks have the rivet code symbol in the head... and may/may-not have the manufacturer's code-symbol [impressed, NOW or just before the finish is applied]
Formed ‘blank's are inspected’ for cracks, straightness, etc.
Heat treatable rivet alloys [AD, D, DD, K/KE] are heat treated to attain specified temper. Nondestructive testing and destructive testing validate the raw production lot.
The Blanks are then cut/trimmed to shank-length and other features added, as per purchase order.
Corrosion-protective finishes are applied, as required per purchase order... CCC$ or Anodize# ...
CCC$ bath applied ‘chromate conversion coating’ [technical term for alodine chemical film].... typically ‘clear to golden-yellowish’ in appearance. This film is micro-thin, soft and relatively easily removed with chemicals... so handle these rivets ‘gently’ to preserve the coating thru installation [bucking]... and they will survive several decades of service.
Anodize# is electrochemical build-up of a super-thin/tough and corrosion/heat-resistant aluminum oxide film... sealed ‘as anodized’ [‘grayish appearance’] or with colored dyes for various ID purposes [applied before/during finish sealing]. Anodize coatings are explicitly applied for enhance corrosion protection in a severe environment... or for color ID/coding... or for shop heat treatment... to be installed by the ‘ice-box method’.
4. D and DD rivets with gray ‘as-anodized’ finishes are capable of being solution heat treated, quenched then driven/bucked ‘as ice-box’ under rigorous conditions [sub-zero storage until driven] to preserve an unstable quenched-temper... ‘W’... that is capable of being deformed with ‘ease’... almost like annealed aluminum... then they naturally/spontaneously re-age to full strength [–T4] temper ‘in-place’ [~96-hours]... and still retain the benefit of the anodized finish which survives the high heat of solution HT/quench... for corrosion protection.
NOTE1.
A. Uniquely, D* rivets [CCC or anodized finish]... with practice, physical effort and sufficient capacity gun/bucking-bar... can be installed [bucked] satisfactorily in suitably ‘hard aluminum alloys’.
5. All other rivet alloys mentioned... A, AD, B, D*, K, KE... are intended to be driven ‘cold [as-is]’ since heat treatment is of no value-added... or would have a high likelihood of permanently 'destroying' the manufactured temper. Without strict process controls most of these alloys will rapidly change their metallurgy and begin uncontrolled migration to a ‘soft’ semi-annealed-state with high heat [as-noted]. Also...
All of these rivets ‘typically’ come with CCC finishes for ‘good-enough’ corrosion protection and lowest cost-per-rivet... or with[less commonly] anodized finishes for unique corrosion environments... with/without unique colors [special dyes] for ID/coding purposes... at significantly higher cost-per-rivet. Rivets with CCC and colored anodize finishes can be exposed to temperatures up-to ~250F-to-300F without damage to the alloy, CCC or dye-colored coating [short term]... but at/above that temperature(range) the CCC film and anodize color-dyes... are damaged by heat/oxidation and become washed-out and useless. .
NOTES2
B. FAA mandates special training for heat-treatment... including HT of rivets and similar parts.
C. IF You still want to apply high-heat to aluminum alloy rivets to soften them for ease of installation be aware that there are NO guarantees of useable strength/stiffness/durability and there would be a total loss of corrosion protection finishes setting them up for in-service corrosion.
D. On a side note, one homebuilt kit manufacturer is offering solid aluminum rivets NOT conforming with any known aircraft standard... their-own design/use... which in my humble opinion is mind-boggling dangerous and ill-advised... for aircraft use.
E. A warning that most are unaware of is that heat treating to –O [annealed temper] results in extreme low strength [expressed in PSI or KSI] ‘NOT TO EXCEED XXX’... means it can’t be any higher strength than XXX... and could be much lower strength than XXX and be ‘OK’ for annealed. For this very reason it is prohibited to use [heat-treatable-for-strength] aluminum alloys in ANY aircraft application... by all authorities [FAA, DoD, etc] and good-sense.
F. CCC, damaged by heat, is a corrosion time-bomb! A serious problem with 2xxx-T4 alloys [AD, D*, DD]... without applied corrosion protection... is a tendency for severe exfoliation corrosion.
G. Colored anodized, damaged by heat, is still OK for corrosion protection... but will lose their color ID [loss-of-value-added cost].
6. WARNING1.
I work at a DoD aircraft overhaul/repair depot... recently discovered that mechanics had installed hundreds of thousands of large diameter ‘AD’ rivets using non-standard riveting-methods resulting in +50% aberrant bucked-installs for ~10-years. After in-depth engineering review we realized that solid rivet installs are considered so self-evident and so standardized and so heavily trained into professional work forces... that discrepancies exceeding small percentages cannot be analyzed... simply never supposed-to-happen. For this reason we have no idea how bad the situation actually is... and it is now considered an ‘airworthiness crisis’ and rework [removal replacement of most/all of these solid rivets] is an urgent priority.
7. Conclusion... aircraft grade solid rivets are precision designed and manufactured ‘parts’ intended for specific strength and durability when installed properly in appropriate holes. Miss-use/abuse can render them worthless... IE dangerous. Use rivets as manufactured/designed and they will provide suitable/durable long-term service.
NOTES3.
H. I’ve been dealing with aircraft aluminum alloys and finishes*** [and their many fabrication processes] for +4-decades. I [mostly] understand the subtle permutations that make each alloy/temper/finish combination useful... or destructive... and how/why to alter these alloys/finishes for specific purposes... and importantly... when NOT to alter them. To me this is familiar territory... but I’m terrible at ‘splainin’ things. Hope this all makes sense.
*** And carbon steel and low alloy steel and stainless steel and magnesium and titanium and copper alloys and their suitable/applicable finishes [and their many fabrication processes]... and how everything fits/works together...
II. I have dozens of solid rivet installation ‘manuals/documents’... it is astonishing that there is a massive lack of consistency and explanation of their uses/do’s/don’ts across the board... so easy to use reliably... but so easy to screw-up.
J. There are unique ways to install rivets that I have ‘learned’ over decades... from the pros... that require training/practice to apply... that come in ‘handy’ when odd situations occur. Two classic examples of unique methods most are unfamiliar with is the ‘the NACA riveting method’... and ‘reverse bucking’... not to confused with each-other.
Sorry... Have-to-go... I wrote most of this reply during a company all-hands-telecon/meeting. I have a laundry-list of homebuiltairplaneforums.com threads I’d love to reply to... but too little available time to do so...
