Lower mechanical properties

[etch]

I have reason to test an Aluminium alloy, grade LM6 as cast. No originally we took test bars from the casting and these were lower than the limits laid down of 80n/mm2 proof, 190 tensile stress 7% elongation.

we originally though that due to the fact that the material was removed from the casting, various defect contributed to the lower values 174 in tensile strength.

next we cast 4 seperately cast test bars in a stell die, and allowed them to cool dow naturally. We then put these bars through x-ray and showed up a spotless, and free from defects, but again they returned values of only 160 tensile strength.

This has got me stumped as to why we are getting consistant results lower than we normally should. Any ideas?

for our american friends, lm6 is equiv to 413.2 i think

Cu 0.1
mg 0.1
si 10.5 -13
fe - 0.5
mn - 0.5
ni - 0.1
zn 0.1

 

[etch]

Just an addition the results for proof stress where double to what we expected and alomost identical to the UTS.

I would appreciate if somone could furnish me with mechanical specs for A413.2, not 413.2 (413.2 has higher iron)

 

[TVP]

Typical properties for alloy 413.0 and A413.0 are as follows:

413.0 A413.0

yield 145 MPa (21 ksi) 130 MPa(19 ksi)

tensile 300 MPa (43 ksi) 290 MPa (42 ksi)

elongation 2.5 % 3.5 %

I cannot imagine that you will ever see 7 % elongation with this type of material-- these properties are what you would expect from a high-silicon aluminum die-casting alloy. I highly doubt that the impurity difference from A413.0 to A413.2 will change the elongation much above 4 %.

Things to consider when mechanical properties are not what they should be: grain size, cleanliness (macro and microinclusions), and porosity (shrinkage and entrapped gas). Are you certain that the x-ray technique you used was capable of identifying small pores, less than 1 mm in diameter? Porosity in die casting can be very small in diameter but contained throughout the cross-section, thereby greatly reducing the strength.

 

[etch]

Cheers TVP

Yes im pretty sure that the x-ray technique is okay, we are certified to detect less than 0.2mm defect in castings for aerospace industry.

Im begining to thinkit might be the machine, the company we use are primarily set up to test aircraft alloys, and i am wondering if its possible that the rate of force applied or length of test could affect results.

Typically results of lm6 give elongation of around 13%. this is the figures stated in the ALARS book, basically the foundrymans bible over here,

Im more concerned as to why the proof stress should be as high as the uts and that the figure is double that of the spec.

I know the material is correct as i poured and tested bath myself.

 

[taila]

I am working in an Auminium Pressure Diecasting.We Manufacture cylinder heads from an AlSi9Cu alloy. Recently we've been getting a lot of cracks on the inner edge of the boss area.They seem to be solidification cracks resulting from hot cracking.The problem is our dies and molten metal are running at the same temperature as usually.Could there be any other reason that might contribute to these cracks other than thermal stresses? Is it possible that the chemical composition or the spray diecoat can be a contributing factor?

 

[Rich2001]

taila
You are most likely experiencing an alloy diffusion problem caused by thermal differences during the cooling phase. Some of the alloy element (notable Si) are moving. Section the item and examine the grain size and composition. Comapre it to samples from the past that you did not have this problem.