1. Tools and materials
The tools include a ring mould and a SiO2 insulating base, see Figure 6. The corresponding specifications and dimensions are shown in Figure 7; a ceramic fiber conical spoon; a graphite stirring rod (about 5 mm in diameter); a furnace capable of maintaining a temperature of 760 °C; a temperature measuring thermocouple; a recording stopwatch and clamps, etc.
The materials are Al99.7 and a corrosive solution: 60% HCl, 30% HNO3, 5% HF, 5% H2O (plastic trough).
Figure.6 KBI Grain Refinement Test Kit
1 - Ceramic fiber base with metal protection ring;
2 - Ring casting mould;
3 - Spoon handle;
4 - Ceramic fiber conical spoon
Figure .7 Typical dimensions of test tools
2. Test method
People engaged in aluminum melt processing and chemical corrosion treatment must have safety protection measures; test tools that contact the melt must be clean and dry; steel ring molds must be coated with graphite and placed on a silica foam base.
⑴ Take reference sample
Use a preheated sampling spoon to take 730 ℃ Al99.7 melt from the test furnace and pour it into a ceramic fiber insulation container, stir for 30s, stop for 30s (1min contact time), pour part of the melt into the ring mold to take a 1min sample, then stir for 30s, stop for 30s, and take a 2min sample. After cooling, the two samples are corroded to check the grain size. If the size is too large, it means that the aluminum and the test method are qualified, and the sample can be used for grain refinement performance comparison.
(2)Take grain refinement samples.
Add grain refiner (usually 0.005% or 0.01% Ti) to Al99.7 melt, and take samples at 1min, 2min or other time intervals in the same way as above. During the solidification of the sample, the side is first crystallized by the steel ring, followed by the bottom, and then the center. Silica foam has very good thermal insulation. The bottom of the cast ingot sample generated by this test is flat and smooth, which simulates the solidification structure of the grains of DC cast aluminum ingots.
(3)Grain size inspection
Immerse the sample in the acid solution of the plastic tank, take it out after about 20 seconds, rinse it with clean water and inspect it. The etching time can be increased or decreased according to the situation. The etched sample can be compared with the reference sample, or it can be measured using the ASTM E 112 81 grain size linear intercept method.
3. Application of the test method
The KBI test method can be used for quality control of the production process of grain refiners in grain refiner manufacturers, and can also be used for inspection or control of grain refinement effects in the casting process of aluminum processing plants. In foundries, it is first used to determine the amount of grain refiners to be added and to regularly inspect the structure of cast products. In order to determine the amount of grain refiners to be added, samples are taken from the furnace or launder used for production, the grain size is checked, and the amount of addition is increased or decreased to achieve a satisfactory grain size. For high-component alloys, the grain size may be very small and difficult to determine visually. It can be checked with a low-magnification binocular microscope. In order to roughly estimate the grain refinement effect, the uneven top of the sample can also be checked. At this time, an auxiliary etching solution is used: 15 parts of HCl, 10 parts of HF and 90 parts of deionized water. After immersion for 3 to 5 seconds, rinse with water until the desired state is obtained. For copper-containing alloys, after this treatment, the residual copper film must be removed by etching with 50% HNO3 solution and washing with water.