Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/06—Making non-ferrous alloys with the use of special agents for refining or deoxidising
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
  • C22C1/03—Making non-ferrous alloys by melting using master alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C23/00—Alloys based on magnesium
  • C22C23/02—Alloys based on magnesium with aluminium as the next major constituent

Definitions

• the present application relates to the use Mg 1-X Al x B 2 to refine the grain size of pure magnesium (Mg) or of Mg-Al alloys and to an associated method.
• Inoculation of melt is the most commonly used method for grain refinement of Mg alloys as Mg has a hexagonal close packed (HCP) structure and it is difficult to decrease the grain size through thermo-mechanical processing due to limited slip systems.
• Zirconium has been found to be an effective grain refiner for aluminium- free magnesium alloys (such as ZE43, ZK60 and WE43).
• zirconium it has not been possible to employ zirconium as a grain refiner for aluminium-containing magnesium alloys (AZ series alloys and AM series alloys) due to the undesirable reaction between zirconium and aluminium forming stable intermetallic phases which adversely effects grain refinement.
• CN101457312 (Shengfa Liu) discloses a Mg-Ti-B grain refiner where an elemental magnesium, titanium and boron powder compact is used to grain refine magnesium alloys.
• WO 2012/110788 in the name of the present applicant employs niobium diboride in various forms as a grain refiner for magnesium alloys (amongst other things).
• WO 2014/027184 in the name of the present applicant discloses the preparation of an Al-Nb-B master alloy for refining the grain of magnesium alloys (amongst other things).
• CN 101457312 A (Univ Wuhan Sci & Eng) discloses the use of compounds such as TiB 2 , AI4C3, A1N, SiC, B 4 C, or TiC to grain refine Mg-Al alloys.
• JP 2002115020 A discloses a method of manufacturing thin sections of a wrought Mg alloy suitable for hot working. Particles selected from the group of titanium chloride, titanium boride, aluminium nitride, titanium nitride, magnesium boride, aluminium boride, molybdenum boride, vanadium boride and aluminium chloride with particle sizes 10 ⁇ or less are dispersed in magnesium in the amount 0.1 to 10 vol.% during the solidification of the base material.
• Material Science Forum, Vol. 710, 2012, p. 161-166 discloses the grain refinement effect of an 96wt%Al-4wt%B master alloy in Mg. It attributes the grain refinement in Mg to the growth restriction factor of Al and the A1B 2 nucleant particles. 'Effects of ⁇ 13 ⁇ 4 ⁇ master alloy on microstructure and properties of Mg-7Al-0.4Zn-0.2Mn alloys' in Chinese Journal of Nonferrous Metals, Vol. 15, No. 3, March 2005, pp. 478-484 reports the grain refinement in Mg-7Al-0.4Zn-0.2Mn alloy by addition of 0.3% ⁇ 13 ⁇ 4 ⁇ master alloy. The grain refinement in this article is assumed to be through TiB 2 and A1B 2 heterogeneous nucleation.
• CN 102383013 A discloses the development of a deformed magnesium alloy containing 2.0-4.0 percent of Al, 0.40-1.70 percent of Zn, 0.20-0.50 percent of Mn, 0.05-1.0 percent of B and the balance of Mg or Mg and impurities.
• the addition of boron could be either in the form of ingot or as an Al-B master alloy.
• Mg 1-X Al x B 2 to refine the grain size of pure magnesium or Mg-Al alloys, wherein x is above 0 and below 1.
• a method of refining the grain size of pure magnesium or of a Mg-Al alloy including the step of employing Mg 1-X A1 X B 2 as a grain refiner wherein x is above 0 and below 1.
• Mg rich boride Mg 1-X A1 X B 2
• Mg-rich boride can be confirmed when A1B 2 is added by measuring the superconducting signature of the Mgi -X A1 X B 2 phase.
• A1B 2 is added to the Mg-Al alloy, wherein the A1B 2 converts to Mg 1-X A1 X B 2 in the alloy.
• A1B 2 is added in powder form (pre- synthesised).
• Mg 1-X A1 X B 2 is the effective grain refining compositions in Mg alloys
• Lattice constants a and c of Mgi -X A1 X B 2 decreases from 3.084 to 3.064 and 3.528 to 3.4466 as x increases from 0 to 0.4.
• Mg based master alloys when used as a grain refiner for Mg alloys, leads to increase in formation of interdendritic grain boundary phase Mg 17 Al 12 , which will limit the ductility of the matrix.
• a weak Mg/Mgi 7 Ali 2 interface will form as the BCC structure of Mgi 7 A 2 is not coherent with the HCP structure Mg structure.
• grain boundary sliding can take place at elevated temperatures due to poor thermal stability and discontinuous precipitation of this phase [4].
• Mg based master alloys is an effective approach to improve mechanical properties in magnesium alloys.
• Mg 1-X A1 X B 2 acts as a heterogeneous nucleating site.
• B 4 C is added to the Mg-Al alloy, wherein the B 4 C converts to Mgi -x Al x B 2-y C y , in the alloy, wherein y>0.
• Mg 1-X Al x B 2 to refine the grain size of pure magnesium or Mg-Al alloys, wherein x is from 0 to 1.
• Figure 1 depicts micrographs of an AM50 alloy showing the grain size when refined by Mg- 5%(Mg,Al)B 2 ;
• Figure 2 depicts what is believed to be the phase transformation of A1B 2 into Mgi -X A1 X B 2 in liquid Mg;
• Figure 3 is a graph showing how the grain size of an AZ91D alloy changes with A1B 2 concentration
• Figure 4 is a graph showing how the grain size of an AZ3 IB alloy changes with A1B 2 concentration
• Figure 5 shows photographs of cooled AZ31B samples with and without grain refining
• Figure 6 is a graph showing how the grain size of an AM50 alloy changes with A1B 2 concentration
• Figure 7 shows photographs of cooled AM50 samples with and without grain refining
• Figure 8 depicts micrographs of an AZ31 alloy and an AM60 alloy showing the grain size when refined by B 4 C;
• Figure 9 shows the superconducting signal for the transformation of B 4 C into Mgi -x Al x B2- y C y
• Figure 10 shows photographs of a billet formed from an AZ3 IB alloy and an AZ91D alloy showing grain refinement from A1B 2 grain refiner precursor;
• Figure 11 shows mechanical test data plots depicting yield strength and elongation for different alloys.
• Example 2 A1B? powder addition to AZ91D alloy
• Example 3 A1B? powder addition to AZ31B alloy
• AZ3 IB alloy is melted in an electric furnace at the temperature range 690-720°C and the melt is held for 1 hour before adding the refiner.
• A1B 2 powder wrapped in Al foil is introduced in the melt and a steel rod is used to push the powder packed foil inside the melt.
• SF 6 +N 2 gas mixture was used to protect the melt from oxidation.
• the mould is a cone-shaped steel mould preheated to 250°C.
• Figure 4 shows that addition of pre-synthesized aluminium boride A1B 2 powder into AZ31 alloy will give a reduction in average grain size with increase in A1B 2 amount. Effect of cooling rate on AZ31B alloy
• Example 4 A1B? powder addition to AM50 alloy
• AM50 alloy is melted in an electric furnace at the temperature range 690-720°C and held for 1 hour after melting. SF 6 +N 2 gas mixture was used to protect the melt from oxidation.
• A1B 2 powder wrapped in Al foil is introduced in the melt and a steel rod is used to push the powder packed foil inside the melt.
• AM50 melt containing refiner is held for 20 minutes before pouring in the mould, which is cone-shaped and preheated to 250°C in oven. It is observed from Figure 6 that the average grain size of AM50 alloy reduces by more than 70% at 0.1% A1B 2 addition levels.
• Example 5 Additions of B 4 C powder to AZ31 and AM60 alloys
• B 4 C boron carbide
• AZ31 and AM60 alloy which are melted in an electric furnace at the temperature range 690-720°C.
• B 4 C powder wrapped in Al foil is introduced in the melt and a steel rod is used to push the powder-packed foil into the melt and the melt is exposed to the refiner for 20 minutes before casting.
• the mould used for casting is a cone-shaped steel mould preheated to 250°C.
• microstructures shown in Figure 8 suggest that at 0.05wt% B 4 C addition, AZ3 IB samples have an average grain size reduction from around 420 ⁇ to 250 ⁇ and that AM60 samples have an average grain size reduction from 420 ⁇ to around 300 ⁇
• AZ3 IB alloy is melted in an electric furnace in the temperature range 690-720°C and held at that temperature for 1 hour before adding the refiner.
• the A1B 2 grain refiner precursor is added to the melt 20 min before casting in a specially designed static direct-chill simulator mould.
• the cylindrical mould is pre-heated to 800°C in a furnace while a Cu-base used for this experiment is pre-heated to 250°C in an oven.
• Macroetching reveals that the bottom of the billet at the Cu-mould edge has columnar grains while the top of the billet has coarse equiaxed grains in the reference sample.
• the grain refined billet gives a uniform distribution of equiaxed fine grains (see Figure 10).
• the experiment is repeated for the AZ91D alloy (also shown in Figure 10).
• MECHANICAL TEST DATA As seen from the mechanical test data plots in Figure 11, an improvement in yield strength and elongation is observed on addition of the selected grain refiners.

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• 2014
  • 2014-11-05 GB GBGB1419715.6A patent/GB201419715D0/en not_active Ceased
• 2015
  • 2015-11-05 EP EP15813478.3A patent/EP3215647A2/de active Pending
  • 2015-11-05 WO PCT/GB2015/053351 patent/WO2016071694A2/en active Application Filing
  • 2015-11-05 CN CN201580060123.7A patent/CN107075613A/zh active Pending

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