To maintain casting quality, it is essential to evaluate how grain refiners and modifiers influence feeding effectiveness.
The EN AC-42100 (AlSi7Mg0.3) aluminium alloy stands out for its excellent mechanical properties and optimal casting characteristics. Inadequate feeding often results in shrinkage porosity, a critical defect in casting processes. This study uses the IDECO thermal feeding analysis system to measure various feeding regions and assess how different grain refiners and modifiers affect feeding efficiency in an industrial setting.
EN AC-42100 is characterized as a hypoeutectic Al-Si alloy, primarily alloyed with magnesium. During solidification, these alloys can contract by 4-8%, leading to the occurrence of shrinkage porosity. Magnesium alloying also extends the solidification range, potentially diminishing feeding capacity. Literature identifies five primary feeding mechanisms during solidification: liquid feeding, mass feeding, interdendritic feeding, burst feeding, and solid feeding.
This work employs the IDECO thermal feeding analysis system to quantify the effects of modifiers and grain refiners on these feeding mechanisms.
Experimental Procedure
Four distinct experiments were conducted at the IDECO technical center using the Rheinfelden EN AC-42100 alloy. Each test involved melting 3 kilograms of the alloy in an electric resistance furnace set to 720 °C.
- Experiment 1: Base alloy without any additions
- Experiment 2: Addition of 63.5g Al10%Sr (targeting 75 ppm Sr)
- Experiment 3: Modified melt with an addition of 32.4g AlTi3B1 grain refiner
- Experiment 4: Base alloy with 32g AlTi3B1 (without Sr)
Thermal analysis samples (approximately 220g) were poured into ceramic molds, where temperatures were measured between 700-400 °C using two K-type thermocouples.
Results and Discussion
The IDECO system successfully calculated the characteristic solidification temperatures for all tests, analyzing cooling curves and their first derivatives.
The addition of strontium (72 ppm) led to a decrease in rigidity temperature and an extension of the interdendritic feeding (IDF) region. The performance of the grain refiner was found to have a less pronounced effect on reducing rigidity temperature.
Three novel equations were generated to quantify the feeding regions:
- MF=(TLIQ-TDCP) / (TLIQ-TSOL) x 100
- IDF=(TDCP-TRigidity) / (TLIQ-TSOL) x 100
- BF=(TRigidity-TSOL) / (TLIQ-TSOL) x 100
Strontium addition enhanced IDF temperature ratios while grain refiner usage also increased IDF ratios, demonstrating their significance in improving feeding behavior. The combination of both additives yielded the most substantial improvements.
This high measurement repeatability and quantitative capability of the IDECO system improve simulations by providing enhanced alloy-specific parameters missing in standard databases.
Conclusion
This investigation assessed the impact of modifiers (AlSr10) and grain refiners (AlTi3B1) on feeding efficiency in the EN AC-42100 alloy. Findings revealed that strontium and titanium independently and collectively enhance feeding capabilities, ultimately facilitating better casting quality.
For contractors and plant engineers, the implications are significant:
- Understanding the role of grain refiners and modifiers can optimize casting processes.
- Implementing findings can reduce the risk of shrinkage porosity in cast products.
- Accurate feeding analysis can improve production efficiency and material utilization.
Source: https://www.aluminium-journal.com/effect-of-grain-refiners-and-modifiers-on-feeding-effectiveness
