Sports Equipment Accessories

Aluminium–magnesium casting alloys have a wide range of application, especially in the automotive and shipborne industry that is directly related to their good mechanical properties.

These alloys are characterised by relatively good castability and are distinguished by excellent corrosion resistance due to high magnesium content. However, application of aluminium casting alloys for structural components requires high strength and suitable high elongations.

Grain size, their morphology, interdendritic distance and distribution of secondary phases are crucial factors affecting mechanical properties of cast parts. The quality of the microstructure of aluminium alloys mainly depends on the chemical composition, melting process and cooling rate.

The grain size of alloys related closely to their solidification characteristics under equilibrium and non-equilibrium conditions. Thermal-derivative analysis (TDA) is much more suitable for industrial applications related to other thermal techniques and TDA method has been successfully used to analyse the features of aluminium, magnesium and zinc alloys in recent years. In this method, the temperature changes in the sample are recorded from wholly liquid to completely solidified phases creating a curve plot of temperature as a function of time.

A cooling curve reflects the release of latent heat of solidification. This release of latent heat in multicomponent alloys changes the slope of the cooling curve which is then used to detect the characteristics of transitions and phase reactions during solidification. The solidification characteristics, e.g., dendrite nucleation and dendrite coherency, can be derived from thermal analysis of the alloy solidification. The dendrite coherency point temperature refers to the state of solidifying alloys at which a coherent dendrite network is established through the formation of grains. Once the dendrites become coherent, liquid metal flow is restricted to interdendritic regions.

Aluminum can be both hot-worked and cold-worked to increase its strength. With the addition of magnesium during the cold-working process, the element increases the strengthening effect. This process involves taking the aluminum and using forging and rolling processes. As the aluminum is worked, more vacancies and dislocations are introduced into the aluminum's matrix structure. These vacancies prevent the atoms from moving about, increasing the aluminum's strength.

During the cold-working process, magnesium is added as a solid solution as it can have a maximum solubility of about 17.4%, although the content rate within most wrought alloys is typically at 5.5%. The magnesium provides moderate as well as high strength characteristics without impacting the ductility of the aluminum alloy. Aluminum alloys with magnesium added are placed into the 5xxx series and are usually made into plates and sheets. While 5xxx aluminum alloys can be extruded, it can be a difficult and costly process.

Magnesium combined with silicon when added to aluminum can be hot worked for extrusion purposes. Aluminum alloys with magnesium and silicon are placed into the 6xxx series. Manganese may also be combined with magnesium as these elements are added to aluminum. However, care must be taken when heat working with added manganese as the aluminum can start to crack during hot rolling.

Magnesium is a common element added to a wide range of alloys because it can add strength without inhibiting the positive characteristics of the base metal. With magnesium in aluminum, the aluminum has added strength, corrosion resistance and good weldability characteristics.