Die casting consists in casting the molten metal in a metallic mould using high pressure (15 - 100 Mpa). This process alloys to produce components with complex shapes and high surface finish in a reduced number of operative passages. Die casting plants are characterized by high automatization capability and high productive cadences. The defects present in some industrial components are investigated and they are correlated to the process parameters. Car components, made of UNI 7363 alloy and electric multifunctional controllers made of UNI 5076 are observed with optical and electron microscope (SEM - EDS). For the components made of UNI 5076, the observation is made on specimens taken during the different steps of the production process (ingot, fusion, degassing and holding furnace). The composition of the alloys is determined using a spectrometer and the EDS technique. Hydrogen contents in UNI 5076 components are determined by the Nitrogen Carrier Fusion Technique. The principal defects observed in the car components made of UNI 7363 are exogen hard points. The EDS analysis carried out on these particles shows that they are oxides of Al, Si, Mg and Ca or intermetallic compounds (Fe-Cu-Ti-Zn-Ni). A piece of slag, taken in the holding furnace shows the same analysis. For the components made of UNI 5076, the observation of the ingot shows numerous impurities. The specimens taken in the fusion, degassing and holding furnaces, show internal cavities due both to gas and to shrinkage. The dimensions and the number of these cavities decrease, but are always present, after degassing. They are visible also in the riser and in alimentation channels. Here are moreover visible non metallic inclusions. The solubility of a gas in a molten metal grows exponentially with the temperature. Hydrogen is one of the most dangerous gas because it has a high solubility in many molten metal for its very small dimension. This solubility decreases drastically in the solid state. Gas porosity is a typical diecasting defect. These cavities are dangerous, particularly in components with sealing characteristics, e.g. valves. It can be seen that hydrogen is present also in the prime materials (ingot) and grows after fusion. Degassing reduces the hydrogen content, but the measured values are high enough to produce gas porosity. Degassing is carried out by nitrogen insufflation. The measured hydrogen quantity grows in the waiting furnace and more remarkably in the diecasted components.


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    Title :

    Studio su difetti nei pressofusi in lega leggera di alluminio


    Additional title:

    Studie zur Fehlerüberwachung von Aluminiumdruckguß
    Study on defects observed in diecasted aluminium alloy components


    Contributors:
    Brotzu, A. (author) / Felli, F. (author)

    Published in:

    Metallurgia Italiana ; 91 , 8/9 ; 55-62


    Publication date :

    1999


    Size :

    8 Seiten, 13 Bilder, 6 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    Italian




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