Simple Solutions That Work! Issue 18

Contact: FRANÇOIS AUDET [email protected] quality indicators specific to the foundry are programmed and optimized in the software as data is generated. Non-conformities are corrected before suffering a scrap episode. PRACTICAL EXAMPLE A foundry concluded they had strontium-related porosity issues in aluminum-silicon alloys. They also decided to stop buying strontium-containing ingots. They used thermal analysis to realize they could only add 120-140ppm of strontium compared to the 180-240ppm of strontium in the new ingots they were buying. Now, they generate less strontium oxides known to nucleate porosities. It’s more cost-effective and accurate to spot check the melt by thermal analysis than metallography (figure 2). While the foundry first wanted to use thermal analysis for eutectic modification, they also generated the data to control grain refinement, secondary phases, etc. CONCLUSION From the 2014 literature review by Djurdjevic with Nemak: ‘’Thermal analysis is used to evaluate the following processing and materials parameters: grain size, dendrite coherency temperature, dendrite arm spacing, level of Al-Si eutectic modification, solid fraction as well as the characteristic temperatures of various metallurgical reactions between liquidus and solidus temperatures.’’ From Geoffrey Sigworth’s talk at CastExpo 2016: ‘’In secondary alloys P (Sb or Bi) can ‘poison’ modification, so thermal analysis is required for Quality Control; 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 out breaks of shrinkage porosity).‘’ Since our introduction of this innovative thermal analysis system, there are now many case studies documenting the ability to better validate melt treatment (and variations) to determine the root cause of casting defects, which has resulted in a reduction of defects and scarp, and increased the production of higher quality parts. 26 Figure 2. A356 metallography before (left) and after (right) grain refinement and strontium additions.