Effects of rare-earth Erbium on grain growth in Al-Mg sintered powder

II. Objective

III. Procedure, techniques and equipment

IV. Results

V. Conclusions VI. Future works

VIII. Acknowledgments

•  Al-Mg series alloys : high ductility, great corrosion resistance, good strength and weldability.

•  Scandium is known to greatly improve strength by forming Al3Sc precipitates that pin grain boundaries, hence inhibiting dislocation movement and improving the material’s hardness.

•  However, the high price of Sc ($270 per gram[1]) is the main problem for the wide application of Al-Mg-Sc alloys.

•  Solution: Erbium; behaves similarly and much cheaper. •  Numerous studies have been made on casted Al-Mg-Er alloys, but

only limited research with powder metallurgy.

•  Characterize the effect of different amounts of Erbium on hot rolled and sintered powder Al-Mg alloys .

•  Compare the two processing methods.

Alloy Preparation HOT ROLLED (HR) •  Get Pure Al, Mg, Er. •  Melt and stir. •  Finally cast in

graphite mold •  Homogenize •  Hot roll

POWDER (P) •  Sieve powder, obtain size distribution •  Use smallest powder for Spark Plasma Sintering (SPS); 5min, 500°C, 50 MPa

Sample preparation

Observation and analysis •  Optical microscope, 100x mag. •  Scanning Electron Microscopy (SEM) •  Linear intercept method on 150 grains (on average), D=S/n (S= length of line, n=number of intercepts)

3. Activation energy for boundary mobility •  Isothermal grain growth equation: Dn- Do

n = K*t (K=temperature dependent constant)

•  Differentiate to get dD/dt=(K/n)*(1/D)^n •  Plot dD/dt vs 1/D on double logarithmic to get K and n

•  Arrhenius: K = A*e^(-Q/(R*T)) •  Linearize then plot LN(K) vs 1/(R*T). Slope is

activation energy Q.

Powder average diameter vs time (coming soon)

1. Hot Rolled (HR) grain size 2. Sintered powder (P) grain size

I. Introduction

Big thanks to Bamidale, Walker and the whole Nain Lab team for their help!

Figure 2. Grain growth in HR samples at 400°C

Francois-Johan Chassaing, Bamidele Akinrinlola, Mathieu Brochu

Table 1. Percent increase in grain size

1. Cutting using diamond saw

2. Aging with conventional furnace

3. Puck mounting, polishing , etching

VII. References

•  Repeat experiments with cryomilled powder (smaller initial grain size)

•  Find optimal weight percent of Erbium •  Reassess activation energy for boundary mobility

1.  “Element Scandium[Click for Isotope Data]." It's Elemental. N.p., n.d. Web. 20 July 2012. <http://education.jlab.org/itselemental/ele021.html>.

2.  Abbaschian, R., Lara Abbaschian, and Robert E. Reed-Hill. "8.22." Physical Metallurgy Principles. Stamford, CT: Cengage Learning, 2009. 244-49. Print.

3.  Callister, William D. Materials Science and Engineering: An Introduction. Hoboken, NJ: John Wiley & Sons, 2006. Print.

Figure 1. Linear intercept method

•  Erbium does inhibit grain growth in Al-Mg alloys •  Processing route changes the effectiveness of Erbium; powder

metallurgy allows for a more even distribution of Al3Er precipitates and hence gives a better pinning of grains

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29  

31  

33  

35  

37  

0   50   100   150   200  

Aver

age

diam

eter

(um

)

Time (h)

Er0.6  Er0.2  

Figure 3.Grain growth in P samples at 400°C

Hot Rolled 350°C 400°C 450°C 500°C

Er_0 45.2% 46.4% 51.5% 53.9%

Er_0.2 31.1% 31.6% 30.7% 35.2%

Er_0.6 28.3% 33.1% 31.2% 39.2%

Powder 350°C 400°C 450°C 500°C

Er_0.2 22.1% 25.1% 24.0% 27.2%

Er_0.6 18.5% 19.4% 19.6% 20.6% 100  120  140  160  180  200  220  240  260  

0   50   100   150   200  

Aver

age

diam

eter

(um

)

Time (h)

Er0  Er0.6  Er0.2  

Figure 4. Optical image of HR sample (Al-5Mg) at 400°C (0 hr)

Figure 5. Optical image of HR sample (Al-5Mg-0.6Er) at 400°C (0 hr)

Figure 6. Optical image of P sample (Al-5Mg-0.6Er) at 400°C (0 hr)

Figure 7. SEM image of Atomized powder (Al-5Mg-0.6Er)

•  Data fits a positive slope indicating a negative activation energy

•  Reason: Other mechanism might dictate grain growth due to presence of Erbium and impurities

y  =  91.058x  -­‐  8.0935  R²  =  0.95462  

6  

6.5  

7  

7.5  

8  

8.5  

9  

9.5  

10  

0.15   0.16   0.17   0.18   0.19   0.2  

Ln(

K)

1000/(R*T)

Er_0.2  

Figure 8. Determining K and n