Fig. 1 a Schematic of taper-shaped graphite mold and thermocouple positions; b Cooling curves of different sections with various diameters in the mold. The inset further reveals the measured average cooling rates

Fig. 2 Positions on the hub, spoke, and the rim regions from where the samples were taken

Fig. 3 Typical optical micrographs of the samples without and with grain refiners at 3 °C/s: a without refiners; b 0.3 wt% AlTiB; c 0.3 wt% RE; d 0.3 wt% AlTiB-RE

Fig. 4 Average grain size with varying refiner contents and varying cooling conditions: a 1.5 °C/s; b 3 °C/s; c 17 °C/s; d 32 °C/s

Fig. 5 a Typical average grain size as a function of the cooling rate for the samples without a refiner and the samples with the addition of different refiners. The addition concentration was 0.3 wt% for each refiner; b Refining effect of different refiners as a function of the cooling rate

Fig. 6 Average grain sizes of different sections of the wheel made of A356 alloy with an addition of AlTiB-RE and conventional AlTiB refiners

Fig. 7 Microstructure of different sections of the A356 alloy wheel with the addition of AlTiB and AlTiB-RE refiners: a spoke with the addition of the AlTiB refiner; b spoke with the addition of the AlTiB-0.11% RE refiner; c spoke with the addition of the AlTiB-0.16% RE refiner; d inner rim with the addition of the AlTiB refiner; e inner rim with the addition of the AlTiB-0.11% RE refiner; f a typical higher magnification of e

Fig. 8 Mechanical properties of the A356 alloy wheel with different refiners