Casting alloys 

Casting alloys of aluminum-magnesium

Aluminum alloys subdivided into wrought and cast. Alloying elements and deformable, and casting the same, but wrought alloys their content is much less.

Casting aluminum alloys

The main alloying elements of cast aluminum alloys are magnesium, copper and silicon. They give a qualitative change in the nature of aluminum alloy. In the alloys Al-Cu, Al-Mg and Al-Mg-Si intermetallic compounds formed, alloys and Al-Si – evtektika. intermetallic compounds, especially when combined with a eutectic, enable the use of different methods of thermal hardening. Other alloying elements – auxiliaries and modifying – is used in much smaller quantities for predetermined improvement of mechanical and physical properties of the alloys.

Aluminum-magnesium alloys

Aluminum-magnesium alloys are single-phase binary alloys with the level of strength from medium to high viscous properties and good. the, they are single-phase, means, that they are not able to increase its strength by heat treatment.

The main feature of these Al-Mg alloys is their high resistance to corrosion, including, in sea water and marine atmosphere. The highest corrosion resistance is achieved with a minimum of impurities - and solid, and gaseous. Therefore, these alloys are manufactured from high quality metals and with special care in its smelting and casting. These alloys are well welded and is often used in construction for decorative. Aluminum-magnesium alloys are easy to machine and has an attractive appearance after anodization.

The alloys are difficult to cast

Compared to the aluminum-silicon alloys, all the alloys of aluminum and magnesium have significantly more problems in casting. They require more careful design of molds and higher temperature gradients during solidification of castings for obtaining good.

During casting these alloys is necessary to consider their increased tendency to oxidation during the melting. It is also important because, that for many articles made from these alloys require a high surface quality and defects, associated with oxides, highly undesirable.

Effect of impurities

  • Copper and nickel reduce corrosion resistance, and plasticity.
  • Iron, silicon and manganese reduce the strength and ductility.
  • Tin reduces corrosion resistance.

Casting alloys series 5hh.h

In US and international classification of aluminum-magnesium casting alloys form a series alloys 5hh.h. Three of them are listed below.

A casting aluminum alloy 514.0

Alloy Formula: 4Mg

Chemical composition:

  • copper: 0,15 % Max;
  • magnesium: 3,5-4,5 %;
  • manganese: 0,35 % Max.;
  • silicon: 0,35 % Max.;
  • iron: 0,50 % Max.
  • zinc: 0,15 % Max.;
  • titanium: 0,25 % Max.;
  • others: each 0,05 %, sum 0,15 % Max.;
  • aluminum: rest.

Typical mechanical properties (as delivered):

  • tensile strength: 145 MPa;
  • yield point: 95 MPa;
  • relative extension: 3 %;
  • Poisson's ratio: 0,33;
  • elastic modulus: 71,0 GPa.

Physical properties:

  • density: 2,65 g / cm3;
  • liquidus temperature: 630 ºS;
  • solidus temperature: 585 oC.

Technological properties:

  • melting point: from 675 to 815 ºS;
  • temperature spills: from 675 to 790 ºS;
  • alloy quarrel - 4043.

A casting aluminum alloy 518.0

Alloy Formula: 8Mg

Chemical composition:

  • copper: 0,25 % Max;
  • magnesium: 7,5-8,5 %;
  • manganese: 0,35 % Max.;
  • silicon: 0,35 % Max.;
  • iron: 1,8 % Max.;
  • nickel: 0,15 % Max.;
  • zinc: 0,15 % Max.;
  • lead: 0,15 % Max.;
  • others: amount 0,25 % Max.;
  • aluminum: rest.

Typical mechanical properties (as delivered):

  • tensile strength: 310 MPa;
  • yield point: 190 MPa;
  • relative extension: 5-8 %.

Physical properties:

  • density: 2,57 g / cm3;
  • liquidus temperature: 620 ºS;
  • solidus temperature: 535 oC.

A casting aluminum alloy 520.0

Alloy Formula: 10Mg

Chemical composition:

  • copper: 0,25 % Max;
  • magnesium: 9,5-10,6 %;
  • manganese: 0,15 % Max.;
  • silicon: 0,25 % Max.;
  • iron: 0,30 % Max.;
  • zinc: 0,15 % Max.;
  • titanium: 0,25 % Max.;
  • others: each 0,05 %, sum 0,15 % Max.;
  • aluminum: rest.

Typical mechanical properties (as delivered):

  • tensile strength: 330 MPa;
  • yield point: 180 MPa;
  • relative extension: 16 %.

Physical properties:

  • density: 2,57 g / cm3;
  • liquidus temperature: 605 ºS;
  • solidus temperature: 450 oC.

magniy-metallmagnesium ingots for alloying of aluminum alloys

Magnesium – aluminum brother

Magnesium is largely similar to aluminum. magnesium Density 20 ° C is 1,74 g / cm³ – it floats in liquid aluminum (density of the liquid aluminum – 2,4 g / cm³). melting point of aluminum and magnesium are almost the same: magnesium has – 650 °C, of aluminum 99,5 % – 657 °C. Therefore, magnesium is directly charged into the melter, Unlike, for example, of silicon. Pure silicon has a high melting point, 1415 °C. For this reason, the silicon is introduced into the aluminum melt is usually composed of silumin with silicon content of about 12 %. Such eutectic Al-Si aluminum alloy melt at a temperature of only about 577 °C.

fazovaya-diagramma-alyuminiy-magniyThe phase diagram of aluminum-magnesium

Sources:

Aluminum and Aluminum Alloys, ASM International, 1996

Aluminum Alloy Castings: Properties, Processes And Applications – J. Gilbert Kaufman, Elwin L. Rooy