I also tested pressure die casted Mg. It gives modulus ranging from 20 GPa to 40 GPa. Moreover, maximum samples showed modulus values above 25 GPa. I read: pressure die casting helps in removing micro pores created due to temperature driven contraction of casting. Does it make difference?
Yes, there are literature available that suggests decrease in modulus with increase in porosity. But effect is mainly felt when porosity level increase beyond 5-8%.
Coming to yield point (calculated through 0.2% secant off set method) it varies from 20 MPa to 80 MPa. I noticed when modulus is near 40 GPa there is more chance to get less yield point. Do comment on this also.
I prepared Mg-.5% Gd alloy through ‘gravity die casting’; strangely, It gave me modulus around 25-40 GPa in most samples. Why this increase is noticed? Intermetallic effect?
Researchers around me suggested 3 reasons:
1) Impurity in Mg.
2) Compliance effect.
3) Porosity issue
But still I am not convinced. Please do comment even if you feel these can only be the reasons. Secondly, Your personal experiences can be of more use to me. Thank You.
Porosity, micro-cracks and foreign phases in the structure (impurities) reduce the modulus of elasticity of all metals. That's a fact. The most well-known example is cast iron, which due to graphite inclusions and pores has a significantly lower modulus of elasticity than pure homogenic iron (about 90-145 GPa against 210 GPa).
Dear Harprabhjot Singh
Magnesium has HCP structure and due to limited slip systems show anisotropy in mechanical properties. Besides the reasons mentioned like 1) Impurity in Mg.2) Compliance effect and
3) Porosity issue, it is highly recommended to do consider the orientation (texture) of Mg-HCP crystal during compression testing. I mean if majority of the HCP crystals have (0002) plans parallel to the surface, you will get maximum value of modulus and values may vary significantly otherwise.
Dear Harprabhjot Singh , In addition to the answer received by you, as per my understanding, this may be due to the process parameter also. In case of pressure die casting the core solidifies later and hence generally the sample for testing purpose are taken from near surface (it is flat type in case of tensile). Further, the defects acceptance is more in case of pressure die casting as such components are prone to slightly more.
I hope this may give you another sight to think and work.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Metals
- Alloys