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    AREA OF INTEREST

  • Magnesium alloys development and castings
  • Structure property correlation of alloys and composites
  • Solidification and grain refinement
  • High temperature behavior – creep
  • Corrosion and coatings
  • Magnesium based biomaterials

Magnesium Activity @ CSIR-NIIST, Trivandrum

Introduction:

Magnesium and its alloys are promising materials, whose light weight advantage could be used for reduction of weight in transports such as automobiles and aerospace. Magnesium, with a density of 1.7 g/cc, which is two third of its counterpart aluminum density (2.7 g/cc) and one fourth of steel density (7.8 g/cc), is the lightest of the structural materials. Magnesium alloys have excellent specific strength and stiffness, exceptional dimensional stability, high damping capacity and high recycleability. However, problems such as low corrosion resistance in general, poor creep resistance (in applications in power train components) and low deformability (in case of wrought magnesium alloys), which restrict its widespread application in automobiles. Enormous efforts have been made in recent years to develop new alloys which posse higher strength and creep resistance and improved corrosion resistance. We have very good expertise in Mg alloy research at CSIR-NIIST as we have been working on Mg alloys for last two decades.

Important Activities/Expertise:

1. Alloy development for high temperature applications
    Alloy modification by minor alloying additions

The most widely used Mg alloy, AZ91 which consists of 9%Al and 1%Zn along with 0.2Mn, show poor creep resistance though it has very good room temperature mechanical properties and corrosion behavior. We modified the microstructure of AZ91 alloy by different elemental additions which provide highly stable intermetallics at high temperature (around 150oC).

Understanding the creep mechanism is important as it helps to develop new materials. We investigated in detail the effects of intermetallic phases on the creep behavior of AZ91 alloy. Thermally stable and finer intermetallic phases such as Mg2Si and Mg3Sb2 are introduced deliberately in AZ91 alloy by the adding Si and Sb.

Development of RE based Mg alloys

Mg-Gd-Zn is one of the interesting magnesium alloy systems as its microstructure consists of different phases depending upon the ratio of Zn and Gd content, resulting in different mechanical and corrosion behavior.  We developed few Mg-Gd-Zn alloys with different Zn and Gd percentages and evaluated their microstructure, mechanical and corrosion properties.

Creep properties of Mg-RE based alloys are much superior to that of commercial Mg-Al based alloys. We investigated the creep behavior and creep mechanism of different Mg-Gd-Zn alloys consisted of different intermetallic phases in them.

2. Solidification studies on Mg alloys
   Grain refinement of Mg-Al based alloys

Grain refinement is an important melt treatment in foundry to improve the properties of alloy castings. Mg shows excellent response to the grain refinement as it is hcp material. Carbon inoculation is a familiar technique for Mg-Al alloys though it has many drawbacks. We investigated cheaper carbon source such as charcoal for the grain refinement of Mg-Al alloys. Other inoculants such as ZnO, B4C were also investigated.

Hot tearing susceptibility studies on Mg alloys

Severe castability problem such as hot tearing can also occur in most of the magnesium alloy castings. When a casting solidifies and contracts under conditions that hinder the free contraction of a part of the casting, hot tearing is likely to occur. Hot tearing is such a complicated phenomenon that a full understanding is still not yet achieved, though it has been extensively investigated for decades. We developed instrumented constrain rod casting (CRC) mould arrangement to investigate the hot tearing behavior of various Mg alloys.

3. Corrosion and coatings
    Phosphate coatings on Mg for corrosion resistance

Phosphate conversion coatings (phosphates based on Mg, Ca, Zn, Ba, Sr, etc.) for Mg alloys are widely explored earlier. However, rare-earth (RE) based conversion coatings for Mg alloys are not studies extensively till now. We developed lanthanum phosphate (LaPO4) coatings on AZ31 (Mg-3Al-1Zn-0.3Mn) magnesium alloy through simple chemical conversion and sol-gel coating techniques for improved corrosion resistance.

4. Mg based biomaterials

Mg and its alloys as biodegradable materials have many advantages such low density, elastic modulus close to that of bone, and biocompatibility and osteogenicity.  The major problem with Mg and their alloys are faster degradation rates and in consequence losing the mechanical properties during tissue healing. There are mainly three approaches followed by researchers to overcome above problems: alloy design, material processing, and surface modification. Recently we initiated research to develop high strength and corrosion resistant Mg alloys and coatings for biodegradable and biocompatible implant applications.

Facilities available:

  1. Mg melting: 500 g to 15 Kg of Mg melting facilities
  2. Secondary processing: Hydraulic press with extrusion die for extrusion of Mg alloys
  3. Microstructure: OM, SEM-EDS, TEM
  4. Phase analysis: XRD, XPS, DTA
  5. Tensile properties: 10T UTM (2 Nos.)
  6. Creep properties: 5T Creep testing machine (3 Nos.)
  7. Hot tearing studies: CRC mould with load measurement unit
  8. Corrosion studies: EIS, hydrogen measurement units, salt spray tester
  9. Coatings: Dip coating unit, Electrodeposition unit
Mg melting tilt
furnace (8 Kg)
Mg melting tilt
furnace (15 Kg)
Mg melting bottom
pouring furnace (5 Kg)
Tensile and Creep
testing machine (5 T)
Salt Spray Tester