Aluminium-silicon alloys

The bath is normally at a temperature in the range 620-710°C, depending on whether the coating material is an aluminium-silicon alloy (for use in high-temperature conditions) or pure aluminium (for corrosion prevention). It is heated by inductors, by resistance heaters or by an external flame. The pot will usually be refractory lined unless cast-iron pots are needed to ensure adequate heat transfer from an external flame. As molten aluminium is extremely aggressive towards ferrous metals, replacement of cast-iron pots is fairly frequent. Refractory-lined pots obviously do not have this drawback, although the bath hardware, in particular the sinker roll and support mechanism, will still be attacked and need replacement at intervals. 

Casting Casting around steel parts, which are first hot dipped in aluminium or in aluminium-silicon alloy (the Al-Fin process), gives good bonding but requires careful design because of the different thermal-expansion coefficients of the two metals. 

Up to 550°C, aluminium coatings may be used in the as applied condition, and the hot-dipped aluminium-silicon alloy may be used up to at least 680°C, but for service at higher temperatures additional diffusion treatment is recommended for all except Calorised coatings. 

Almond shell Aluminium, atomized Aluminium, flake Aluminium-cobalt alloy Aluminium-copper alloy Aluminium-iron alloy Aluminium-lithium alloy Aluminium—magnesium alloy Aluminium-nickel alloy Aluminium-silicon alloy Aluminium acetate... 

Sensing sodium The /1-aluminas (see Section 4.5.3) can be successfully exploited as a sodium sensor. Sodium is widely used in the metallurgical industry, for example for removing arsenic and antimony from zinc and lead, for removing the same two elements and oxygen from copper, and phosphorus from iron. It is also added to aluminium-silicon alloys to control microstructure and, in consequence, mechanical properties. 

Kuljanic E, Soitino E (2005) TWEM, a method based on cutting forces - monitoring tool wear in face milling. Int J Mach Tools Manuf 45 29—34 Ng E-G, Szablewski D, Dumitrescu M, Elbestawi MA, Sokolowski JH (2004) High speed face milling of an aluminium silicon alloy casting. CIRP Ann Manuf Technol 53(l) 69-72... 

Aluminium-silicon alloys are used for the brazing of aluminium and aluminium alloys. The composition of a commonly used aluminium brazing alloy is shown in Table 12.4. 

Pratskov DV, Filippenko AV, Artemenko SA et al (1989) Method for productimt of aluminium-silicon alloys. USSR Patent 1505076, 1 May 1989 1600392,15 June 1990... 

The pitting depth on aluminium-silicon alloys does not exceed 200 p,m after 10 years of exposure to marine or industrial atmospheres [11,12]. The stress corrosion resistance of 42000 (A-S7G) alloys is excellent [13]. 

Phosphorus is technologically and economically important in aluminium-silicon alloys. On one hand it regulates the mechanism of solidification of eutectic (12.5 % Si) and nearly eutectic alloys, on the other hand it grain refines the primary silicon in the hypereutectic system (15-25 % Si) When the eutectic or nearly eutectic aluminium-silicon alloys contain less than 5 Mg/g of phosphorus, the alloy solidifies into a lamellar structure. When the phosphorus concentration is above 9 Mg/g a globular structure is obtained. In hypoeutectic alloys with about 7 % of silicon, the solidification is only fine lamellarly at phosphorus contents between 2 ig/g and 4 g/g. When magnesium is present, even below 2 ng/g a globular structure is obtained. 

Most of the aluminium-silicon alloys are cast in a modified state whereby strength and elongation are improved. Phosphorus consumes however modifying agents (sodium or strontium) an eutectic alloy containing 10 to 15 Aig/g of phosphorus needs about 45 to 50 fig/g of sodium. It is therefore a matter of economical necessity to dispose of accurate methods for the determination of phosphorus in aluminium-silicon alloys (4). 

Critical investigations (2) (25-27) have shown that none of these processes are sufficiently selective. It has been found that certain aluminium-oxygen compounds are converted partially in exactly the same manner as metallic aluminium. Other aluminium compounds, particularly in aluminium-silicon alloys, remain in the isolation residues to a certain extent and are thus incorrectly determined as oxygen. Residues of metallic aluminium must also be expected in the fractions isolated. 

As has been shown by initial comparison tests with activation analysis techniques under the auspices of Eurisotop and BCR Study Groups, good results are obtained with aluminium-silicon alloys - free from magnesium or only containing less than 3000 pg/g of it - if reducing fusion in a stream of carrier gas is employed in the manner suggested by Kraft and Kahles (47) for the analysis of unalloyed aluminium, with the sole difference that the reaction temperature is increased to 1950°C. Like for unalloyed aluminium, the oxygen contents reported are near the detection limit, and only increase to values of a few pg/g at silicon contents of 7 % or more. 

Phosphorus concentrations in aluminium-silicon alloys range from a few Mg/g to some 10 ig/g. Problems concerning the determination of phosphorus are less related to the analysis itself, than to the preparation of the samples. 

Table VIII-3 gives some results for phosphorus in aluminium-silicon alloys of different origins with different silicon concentrations. The results obtained with and without etching after irradiation do not differ significantly. The standard deviation ranges from 1 to 24 % with an average value of 6 %, for phosphorus concentrations between 1.7 and 25 g/g. The results...

Table VIII-3 Results for phosphorus in aluminium-silicon alloys ( g/g)...

The only - preliminary - intercomparisons carried out in the frame of BCR concern phosphorus in an aluminium-silicon alloy containing 12 % silicon. Results obtained using both classical and nuclear methods (Table VIII-5), indicate that precisions and accuracies of the order of 10 % are generally... 

Commercial filler metals are aluminium silicon alloys containing from 6.8 % to 13 % silicon. 

Pan] Panseri, C, Guastalla, B., Investigations on the Permanent Modifieation of Euteetie Aluminium-Silicon Alloys. I.-Influence of Titanium Additions as the Third Component (in Italian), 10(5), 202-227 (1941) (Phase Diagram, Experimental, Review, 161)... 

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