Explosion surfacing of mg alloys with aluminium and CrNi austenitic steel.

Trso, Martin ; Turnova, Zuzana ; Nesvadba, Petr 等

1. INTRODUCTION

Present technical practice nowadays often employs joining of materials with different chemical and physical properties (Nesvadba, 2007). There is in many cases endeavour to attain, that one of materials (metals) would in optimum measure meet the requirements laid on chemical, physical and mechanical characteristics desired for a certain application (Turna, 2007). The proportion of application of diverse technical materials is shown in Fig. 1.

2. MAGNESIUM ALLOYS

Magnesium and its alloys are very interesting materials for technical practice, mainly for the field of transport technology. Commercially used magnesium alloys have specific weigh around 1 700 kg.[m.sup.-3], what is by about 35 % lower value than in case of Al alloys and by 75 % lower than in case of steels. Chemical composition of AZ 91 alloy is shown in Table 1.

3. EXPERIMENTAL

Used materials: AZ 91, AZ 63, technical Al (99.5 %), CrNi austenitic steel (18Cr8Ni). Accelerated materials were Al and CrNi austenitic steel.Parallel location of welded materials and Semtex explosive was used in welding. Weld edges were mechanically machined and degreased prior to welding. The quality of welded joints was assessed by:

* ultrasonic defectoscopy

* optical microscopy (by the study of macrostructure and microstructure)

* microhardness measurement across the bimetal boundary

* X-ray microanalysis of the zone of bimetal boundary.

Figs. 2 and 3 show the macrostructures of 18Cr8Ni-AZ 91 (Belokostolsky, 2007) and Al-AZ 63 (Demianova, 2007) bimetals and Figs. 4 and 5 show the microstructure of mentioned bimetals.

[FIGURE 2 OMITTED]

[FIGURE 4 OMITTED]

Microhardness measurement was performed across the boundary of combined joint Al--Mg alloy type AZ 63. Location of indents in microhardness measurement is marked in Fig. 6. The values of measured hardness are plotted in graph (Fig. 7).

[FIGURE 6 OMITTED]

X-ray microanalysis was performed on energy-dispersion microanalyser type JEOL JXA-80 at FCHPT STU Bratislava. Structural situation in the boundary zone of bimetal was studied in details. Figs. 8 and 9 show: situation of line microanalysis and the courses of concentration change of Al and Mg over the bimetal boundary.

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

[FIGURE 9 OMITTED]

4. CONCLUSIONS

The aim of work was to suggest the technology, parameters and conditions of explosion welding Mg alloy type AZ 63 with aluminium and austenitic steel type (18Cr8Ni) with magnesium alloy type AZ 91.

Quality of joints was assessed by defectoscopy and metallographically. Macrostucture and microstructure was studied and microhardness measurement in joint boundary was also performed. Very good quality of joints was attained in case of Al - AZ 63 bimetal. An undulated boundary in direction of detonation speed [v.sub.d] = [v.sub.k] (welding speed) was observed, which is the guarantee of quality joint.

Boundary quality was in details assessed and proved by X-ray microanalysis.

In case of austenitic CrNi steel--AZ 91 alloy combination it is still necessary to optimise the parameters and conditions of welding.

This work is a part of VEGA no. 1/3191/06 project.

5. REFERENCES

Belokostolsky, T. ; (2007) Design of welding technology for joining Mg alloy with selected metals. Thesis, Welding Department at UVTE , MTF STU, Trnava.

Demianova, K. ; (2007) Design of welding technology for joining Mg alloy with aluminium. Thesis, Welding Department at UVTE , MTF STU, Trnava.

Middeldorf, K. ; Herold, H. ; von Hofe, D. ; (2005) Trends in Joining. IIW International Conference Benefits of New Methods and Trends in Welding to Economy, Productivity and Quality, Czech Welding Society, Prague.

Nesvadba, P. ; (2007) Explosion welding. Lectures presented at FS VUT Brno.

Turna, M. ; (2007) Special methods of solid state welding. Lectures presented at IWE. FS CVUT Prague.

TURNA, Milan, Supervisor, Mentor

Table 1. Chemical composition of AZ 91 alloy.

 Chemical composition (wt.%)

Mg Al Zn Mn Si

base 8.3-9.7 0.35-1.0 Min. 0.13 0.50

Mg Cu Ni balance

base 0.10 0.03 0.30

Fig. 1 Percentage proportion of technical materials used in
practice (Middeldorf, et al., 2005).

Steel 21%
Aluminium 39%
Magnesium 8%
Plastics 6%
Glass-Ceramics 5%
Multi Materials 17%
The rest 4%

Note: Table made from pie chart.