You know that testing for leakage, mechanical properties or X-Ray won’t avoid suddenly scrapping your aluminum castings. We can pray but it’s too little too late : we need to work with liquid metal and mold control before casting, not just tests on the solid casting. And ASTM standards won’t help us much on reaching your energy efficiency and low scrap rate objectives. Best practices and data will. This article offers a sneak peak of the 2016 MODERN CASTING survey on melt control practices ( figure 1 ). Then a word on thermal analysis for liquid aluminum quality control. Simply, why spectrographic analysis is not enough to make good money out of your melt. In the end, you’re getting your foundry more and more into John Campbell’s bifilm code , right?
Click here to the SFTA Thermal Analysis page :https://www.solutionsfonderie.com/thermal-analysis/
To casting simulation page : https://www.solutionsfonderie.com/simulation/
Figure 1 : 50 AFS foundry members’ responses to the question : ” When do you most add eutectic modification relative to other additions ”? (MODERN CASTING, November 2016), full survey available here https://www.moderncasting.com/issues/2016/11
Is figure 1 still useful to you ? The argument on best practices for aluminum castings is not over still in 2023. Our approach is to measure your melt and take decisions based on data.
SFTA Thermal Analysis to avoid scrap episodes
At CASTEXPO2016 in Minneapolis, you also listened like we did to Geoffrey Sigworth speaking on thermal analysis for aluminum foundries :
” •In many foundries alloys are modified to shorten solution heat treat times (savings: 3-4 cents/lb, plus increased heat treat capacity)
•In primary alloys, Sr analysis is usually adequate to ensure modification.
•In secondary alloys P (Sb or Bi) can ‘poison’ modification, so thermal analysis is required for QC
•In Cu-containing alloys over modification (Sr + Ca) can cause undesirable ‘blocky’ Al2Cu phase to form. Thermal analysis can prevent this.
•Thermal analysis helps to track down ‘problems’ (e.g., sudden otbreaksof shrinkage porosity)
•A quick (5 minute) test establishes the grain refinement and modification in a casting
•LPP is probably a better grain size parameter, and should be incorporated in a commercial test.
•In Cu-containing alloys the eutectic temperature (by itself) is no longer a reliable indicator of modification. An improved analysis is desired (along the lines of LPP?).”
The figure below shows the effect of strontium additions on A356. Watch out for strontium oxides building up over time as you remelt, which could lead to unexpected porosities. Do you want to use less expensive ingots and still have a perfect casting?
Bifilm code :
The main idea is to avoid creation of oxide bifilm and entrainment into our castings ( figure 2 ). The ideal consists in having clean scrap or ingot, not create bifilm defect in the furnace while melting, have a way to clean the melt and finally, fill our molds without entraining these oxide defects into the casting as it solidifies. If you don’t have bifilm defect in your melt, we’ll nucleate less porosities in the solid parts. Filling practices and mold filling system designs are paramount, but first we need a clean melt with correct metallurgical properties in the furnace before casting. Let’s see how we should treat the melt and save on energy.
Figure 2 : Sketch showing the formation of a double oxide film defect [John Campbell].
Ask your SF metallurgical engineer to measure your melt properties using our probes below:
- SFTA Thermal Analysis of non-ferrous alloys;
- HYCAL for dissolved hydrogen in aluminum;
- QualiFlash for aluminum melt cleanliness level;
- AluLIBS and GalvaLIBS for live melt chemistry and replace the lab;
- 100% X-Ray analysis before machining;