Luoyang Judian Metal Hot Processing Equipment Co., LTD is mainly engaged in the manufacture of complete sets of equipment in the metal thermal processing industry and the integration of the entire production line.
Chemical Composition Adjustment in Aluminum Ingot Production
Effect of Magnesium Content on Crack Tendency in 300 mm × 1200 mm Slab Ingots
Learn why chemical composition adjustment is required in molten primary aluminum, how magnesium content affects slab ingot cracking, and what factors influence batching accuracy.
The following data shows the influence of magnesium content on the crack tendency of 300 mm × 1200 mm slab ingots.
Magnesium Content / %
2.7-2.8
2.68
2.64-2.66
2.62-2.63
2.59-2.61
2.55-2.58
2.43-2.46
2.38-2.41
2.32
Rejection Rate Due to Ingot Cracking / %
0
0
7.4
16.4
17.43
11.5
41.5
37.5
76.5
1. Why Is Chemical Composition Adjustment Necessary?
The adjustment of the chemical composition of molten primary aluminum is mainly required for the production of aluminum ingots for remelting, such as Al99.90-Al99.00, Al99.7E and Al99.6E; refined aluminum ingots for remelting, such as Al99.996-Al99.95; and industrial pure aluminum ingots for pressure working, namely the 1xxx series.
The aluminum content of 1xxx industrial pure aluminum ingots corresponds to the purity range from refined aluminum ingots for remelting to ordinary aluminum ingots for remelting, that is, Al99.996-Al99.00. These aluminum ingots can all be produced directly from molten primary aluminum.
The chemical composition of molten primary aluminum in electrolytic cells is not always completely consistent. However, the grades of cast finished products are different, and each grade has strict requirements. In particular, industrial pure aluminum ingots have stricter chemical composition requirements to ensure that the processed aluminum products meet the required performance standards. Therefore, the chemical composition of molten primary aluminum must be properly adjusted.
Industrial pure aluminum has no tendency to form cold cracks. However, within the specified chemical composition range, if the composition and impurity content are not properly controlled, hot cracks may form due to high hot brittleness.
For industrial pure aluminum, the main method for reducing hot brittleness is to control the contents of iron and silicon impurities. Under a normal casting system, when the titanium content in the alloy is 0.01%-0.02%, production practice shows that if the silicon content is less than 0.3%, controlling the iron content to be 0.02%-0.05% higher than the silicon content is sufficient to eliminate the hot-cracking tendency of cast ingots.
When the silicon content is greater than 0.3%, the influence of the iron-silicon relationship on hot cracking becomes less obvious. This may be because, as the total amount of iron and silicon increases, the amount of non-equilibrium eutectic formed during crystallization also increases.
A common explanation of the influence of the iron-silicon ratio is that when the iron content in the alloy is higher than the silicon content, crystallization proceeds within a relatively narrow temperature range in the form of a peritectic transformation.
Additional Batching After Intermediate Analysis
During batching, if the product grade needs to be improved, high-grade aluminum ingots should be added. If the product grade needs to be lowered, low-grade aluminum ingots should be added.
After batching, if the intermediate analysis value cannot meet the specified value, additional batching must be carried out. The calculation method is the same as above. The commonly specified center value is used as the calculation standard for correction.
Let:
a = amount of primary aluminum charged into the furnace
b = standard value
c = intermediate analysis value
d = amount of master alloy added for correction
e = alloying element content in the master alloy used for correction
The amount of master alloy d required for correction is calculated as:
d = [a(b - c)] / (e - b)
2. What Factors Affect Batching Accuracy?
The factors affecting batching accuracy mainly include the following:
The grade of molten primary aluminum in the electrolytic cell is determined according to the pre-analysis result from the day before aluminum tapping. If the purity of the molten primary aluminum in the electrolytic cell fluctuates sharply, the purity of the aluminum liquid after batching may easily exceed the specified value.
When aluminum is tapped from multiple electrolytic cells into one ladle, a large error in the tapping amount from each individual cell will affect batching accuracy.
Errors in the amount or purity of the added master alloy may cause the purity of the aluminum liquid after batching to exceed the specified value.
Fluctuations in the chemical composition of returned scrap will also affect batching accuracy.
3. How Should Excessive Aluminum Liquid Purity Be Corrected When Producing Aluminum Ingots for Remelting?
When producing aluminum ingots for remelting, if the purity of the aluminum liquid after batching exceeds the standard and the mixing furnace has not yet been filled, the amount of molten primary aluminum added can be adjusted according to the charged aluminum liquid amount and the intermediate analysis value of the chemical composition.
The content of the relevant element in the additionally added molten primary aluminum should be lower than the standard value. The amount of molten primary aluminum to be added can be calculated as follows.
Let:
a = amount of primary aluminum charged into the furnace
