Do you only want to repair the "stress cracks", or do you want to join the steel insert to the aluminium?

If you want to join the steel insert to the Al, then theoretically, you can not weld them together because their melting points are too far appart. (Not to mention the problems with intermetallics that will form.) I suspect that this is not really your intention, so I will not say anything further about this. If this is infact your intention, let us know because I may be able to give you a couple of pointers using a combination welding/brazing technique that I once used to join Copper to Al.

If it is merely the repair of the casting base material, this should not be too difficult in theory, but you will have to give us more info. There are many different Al casting alloys. Many of them are however based on a 12% Si content, because it is at this composition where the lowest probability of cracking occurs. (Is the eutectic composition of Al-Si.) If you therefore just want to "go for it" and throw the casting away if it does not work, I would use a filler with typically a 12% Si content, or something close. If my memory serves me right, above 5% Si content should be quite weldable.

If this is a critical job, give some more info regarding the casting chemical composition or the material spec. Then I will take the trouble to look it up in the literature that I have.

Just another thought: What do you mean by "stress cracks"? Are they fatigue cracks? If so, the repair should not be too difficult, but would probably not last too long in service unless you change something to your system. Are they Stress Corrosion Cracks (SCC)? If so, it may be very difficult to actually remove the affected material because it tends to be very insiduous and penetrate the material in fine branched cracks all over. When you then start welding, it appears as if the crack just keeps propagating.

Regards
Niekie

As correctly stated above, without specific information identifying the material type of your casting and some general information about the geometry of it, it is only possible to give the most general rules of thumb. At this point its impossible to responsibility offer advice regarding filler wire, pre heat, stress relief, distortion and restraining fixtures.

If I understand your problem correctly (cracks in the casting radiating out from ferrous bearing races). The best way to go-and this is true for studs, bearings and helicoils, is to chase down the entire crack by routing out 100% of the crack and verify with dye penetrant inspection. Now this will most likely necessitate the removal of your ferrous insertions. Operating conditions for most of these castings include oil or hydraulic fluid, if that fluid remains in the crack or heat affected zone you are going to risk even bigger problems. If you were to remove the bearing race do you have access to a machine shop to remachine and refit a new one? If you don't than greater creativity will need to be employed and chances for long term viability decreases.

Let us know more


Lawrence