Conrod Aluminium Alloys ?

[GT52]

The last conrod thread has been archived and thank the member SWALL (materials) who responded to my enquiry regarding
RSA-707 T6 and it's apparent low notch toughness, though thread cannot be viewed anymore I decided to start a new one.
I know a few aluminium rod manufacturers have used 7075 T6 over the years but with a UTS of only 550Mpa I believe there may be a better alternative out there.
There are many factors to consider in selecting a connecting rod material,and to find the best material out there we may need to consider many properties including:
Hardness, Tensile, Toughness, Fatigue, Creep & Stress Rupture, Compressive & Shear e.t.c
Some manufacturers also seem to claim 20% more tensile and yield strength ... Type of forging ... heat treatment ?
It will be interesting to hear your thoughts on this topic.

 

[GT52]

Does anyone out there know if 7068 has been used in conrods ?
With a T6 temper it's UTS is @ 710 MPa & an increased Brinell hardness @ 190.

 

[GT52]

What would be the best stress relieving process that could be carried out on such an aluminium alloy conrod and at what time in the manufacturing process should this be applied to be effective ?

 

[Tmoose]

I'd be looking at the endurance or fatigue strength of the alloy at operating temperature rather than the UTS. I'd also be analyzing the heck out of the rod geometry to (1) keep the big end round and (2) minimize stress concentrations that can secretly steal a component's strength and life.

 

[marinop]

I too am interested in aluminum Alloys for con rods. I'd like to manufacture some rods for motorcycle use. Old Brit bikes come with forged alloy rods.

I have looked into using 7075, 7175, 7068, C405 etc. all of these alloys are tough but when subjected to heat the strength goes away ans goes away very rapidly. Aftercontacting Alcoa and Kaiser engineers I came away frustrated as they want to help but are totally unfamiliar with there own products as not much real testing has been done to veryify the correct alloy along with it's heat treat to accomadate my concerns.

Question has anyone out there have an idea of where I can go to not only get the corrrect infomation but the correct alloy? I have contacted automotive manufacturers with their "proprietary" alloys but none will confirm use in an air cooled engine. Any help will be appreciated greatly.

 

[kenre]

In R/c racing 2 stroke engines i have been using 2024 T351.
Not as high a strength as the other alloys mentioned, but superior strength at elevated temps.

Ken

 

[marinop]

Hi Kenre,

Have you calculated the stresses on the rod for your application? According to the engineer at ARP who designed out bolts at 8000 rpm got the dynamic load of 8600 lbs.

No engineer that I've spoken with want to stick out his nec and commit, especially those at Alco and Kaiser but the "ideas" are everywhere on the spectrum. C405, C415, 7068, 2024 but in T851, 2099-T83, 2014, 2618 etc. are being touted but when making a few hundred mistakes get costly.
Then we have the group that only a forged product has a chance!

any more ideas welcome

regards
Marino