6005-T5 for marine extrusions

[grob]

Does anyone have experience with the Alloy 6005-T5 for marine extrusions, an extruder is reccomending it instead of 6061-T6. I have not heard of it, and looked up the specs on Matweb and it seems ok.

Gareth

[Ad Hoc]

As always, depends upon the application and whether it is to Class or not.

I have used 6005A many times, successfully too. It is often used when complex shapes become more difficult to extrude, since 6005 is "easier" to extrude. However, despite its better extrudability, it has 3 times as much copper content compared to the more "usual" 6082, as such LR don't allow this below the waterline.

In addition to this, LR has found (in-service conditions) that 6005A is more brittle than 6082. Hence for extrusions such as Bulb Bars, these will be more prone to exhibiting micro cracks went formed for high or complex curvature, owing to its lower ductility. Hence the fatigue of such structural members will be reduced accordingly. Since the existence of microcracks from the forming of the extrusion will be sites of crack propagation, rather than crack initiation.

Using magnesium based filler wire (5356), rather than silicon based filler wire (4043) on 6005A increases it's strength, ductility and fracture toughness.

[grob]

Thanks for the reply,

According to Matweb.com both 6082-T6 and 6005-T5 have the same amount of copper at 0.1%. Do you think this is wrong?

The extruder suggested we consider it as it is easier to extrude and so will be cheaper.

Thanks

Gareth

[Ad Hoc]

Grob
Sorry when i pressed send, looks like a line went missing. I was referring to the fact that 6061 has some 3 times the copper, but is often used instead of 6005A, as a comparison. Hence that line..as you are indeed correct 6005 and 6082 have approx 0.1% copper each.
Sorry about that....dunno why my webpage did that?

[mydauphin]

Don't use underwater... or area that is wet like bilge. Fine for interior or superstructure if prep and painted.

[grob]

Don't use underwater... or area that is wet like bilge. Fine for interior or superstructure if prep and painted.

Are you saying don't use 6005 underwater, if so why not?

Gareth

[mydauphin]

Yes, don't use it. You should use only marine grade aluminum such as 5000 series. Long term the 6000 series will disappear. It can be use above waterline if properly prepared and painted and for things like trailers that are not in water all the time.
http://www.solsteel.com.au/Alloys.htm go down to
Corrosion Resistance
6xxx series marine grade alloys are fairly resistant to marine environment corrosion. However they should not be used in exposed conditions (immersed in seawater)
Also check out:
http://www.saltinstitute.org/symposia/symposium1/lowe.pdf
5000 series is much better. 6005a has 3times the copper of 6005 and 5086.

Anyway an aluminum boat can be a nightmare, or a blessing, but you really have to know your metals, galvanic corrosion, electrolysis and make sure your electrical is done correctly or your boat will disappear before your eyes. Talk to a marine boat builder, not a person selling AL.

[Ad Hoc]

mydauphin
Agreed. I was advised many years ago by LR not to use 6005a below the waterline.

I should also check my typing late at night time too...i miss type too much, sorry about that. All the 6's and 0's get messed up after too much wine....doh! I should recheck before i click send.

I started my love-hate relationship with aluminium around 20 years ago. Designed a 45m monohull using the "latest" technology as of then. All extruded planking. The whole hull was constructed with extrusions, including the shell plate with 'built-in' stiffening. Didn't take long to discover the mistake in using the "latest technology"..!!

[simon]

Ad Hoc,

I would be interested in hearing your approach with building in extrusions. Could you explain a bit more the approach and the extrusions you used?
What were the mistakes and effects?
Could it be improved?
What were the advantages, less building time, strength?

Regards

Simon

[Ad Hoc]

Simon
Extrusions, such as plate and stiffener attached, are great for large flat areas. These can be automatically welded too. These are very good for deck structures and as such not so prone to lesser quality alloys if you're not fussy, if internal. If external, then 6082 is the preferred.

For internals, obviously Tee sections in deck houses and superstructures are ideal.

For hulls, bulb bars for long.t stiffening, all internal, do not use externally if below the waterline. If you design the hull that can utilise extrusion Tee's as main transverse frames, then that saves on production costs. But, the hull design is a compromise, like everything, so you need to check your EHPs etc first.

Mistakes:- poor detail design and ignoring fatigue!. Also incorrect filler wires or grades of alloy and ignoring effects of bimetallic corrosion.

Overall, the key to using extrusions is not to get carried away with their "simplicity". Horses for courses, and never forget that these are 6000 series alloys, heat treatable, and not 5000 series. (Unless you have shed loads of money for some 5000 series extrusions). 6000 series behave differently and have their limitations compared to 5000 series.

As always, its in the detailing...in both the dessign and manufacture