Gravity Sand Cast - Investment Casting LM25TF 2

[hydromech]

Hello All,

Can anyone give me the benefit of their experience with casting LM25TF?

Is there any difference between the material properties that is caused by the different cooling rates between gravity sand casting and investment casting? There is subsequent heat treatment after each process, does this TF process bring them back to the same level.

I have a customer that is concerned about how the lack of controlled cooling on investment casting affects the grain structure.

Can anyone help?

Thanks in advance

Adrian

 

[swall]

This alloy is commonly known as AA alloy 356 and the TF designation makes it 356-T6. The final mechanical properties are established by the T6 heat treatment, not the casting process. This alloy, in the sand cast version, is given an A rating for some of the significant castability traits, such as resistance to hot cracking and solidification shrinkage. This will be potentially negatively impacted in an investment process, where hot tearing and shrinkage could arise because of the lack of directional soldification. This all depends on casting configuration, particularily section size. You need to talk to a both sandcast and investment casting houses about the casting design in order to have an intelligent conversation with your customer.

 

[TVP]

Adrian,

Fatigue life of aluminum castings is controlled first by defects (porosity, oxide films) and in the absence of those, then by microstructural details (secondary dendrite arm spacing or SDAS, eutectic modification, etc.). Qigui Wang from GM Powertrain has probably done the most work to isolate some of the effects of solidification time on SDAS and subsequent fatigue properties. His work has been published in SAE Technical Papers as well as journal articles, and following link has a summary of some research conducted together with Diran Apelian at WPI. Figure 3 shows the difference between A356-T6 that has SDAS of 20-25 µm vs. 70-75 µm.

http://www.wpi.edu/academics/Research/ACRC/Research/14.html

 

[swall]

Excellent, TVP. Do you know if Wang's work at GM was lost foam specific?

 

[TVP]

Wang's work is not specific to the lost foam process, although that is obviously one of the processes that has been investigated. In order to evaluate a number of different processes and their associated microstructures, other trials used samples obtained from chill-cast sand molds and wedge-type (varying thickness) permanent molds. Alloys investigated include 319 and 356. Here is a link to Google Scholar showing some of the journal articles, etc.

http://scholar.google.com/scholar?a...s_sdt=1.&as_sdtp=on&as_sdtf=&as_sdts=23&hl=en

 

[hydromech]

Thanks to you all for your help.

Regards

Adrian