Economical technology for joining dissimilar materials in automotive industry.

Popescu, Mihaela ; Magda, Aurelian ; Mocuta, Emilia 等

The paper's authors presented the latest experimental results for dissimilar joining galvanized steel--aluminium alloy, achieved through the new CMT procedure. The latest endowments of Mechanical Faculty have proved their efficiency through the high accuracy results obtained. The researchers want to apply new welding technology results, in order to obtain favourable economic impact, identifying the settlement in automotive field. On international framework, these preoccupations are much updated. The results are original, developed in the frame of the faculty, using trial programs, and using trial equipments of UPT laboratory Renar authorized. The scope is to develop the joining technology obtained and to use it in automotive industry with real economic effects.

Key words: CMT, dissimilar joining, automotive, low heat input

1. INTRODUCTION

The combination of different materials (dissimilar, heterogeneous or black-and-white materials, as they are also known) is a permanent problem because of its implications. In the current automotive industry, the problem is the combination of galvanized tables with aluminium alloys, problem that can be satisfied by using the approved process by Fronius called Cold Metal Transfer CMT (Bruckner, 2005).

2. JOINING OF DISSIMILAR CMT, GALVANIZED TABLES-ALUMINIUM ALLOY TABLES

In order to create appropriate technologies of conjunction, there have been developed complex and experimental programmes with interdisciplinary participation of specialists. The experiments were focused on the achievement of dissimilar conjunctions, galvanized table- aluminium alloy (Staubach, 2007), with the Fronius Trans Pus Synergic 2700 CMT installation, with final welding parameters, as indicated in table 1. In order to establish optimal welding parameters, it was imposed to know the exact chemical composition of the base materials. This was established with the assistance of the Optical spectrometry method, using emission spectrometer from the Material Science and Welding Department of Mechanical Engineering Faculty, in "Politehnica" University of Timisoara.

This is how the percentage concentration alloy-aluminium board and the percentage concentration steel plate was determined (table 2 and table 3).

In order to ensure a proper examination, the sample has to be prepared in this way (Lutz, 2007): it has to be included in duracryl, in order to be processed Metallographic, after that it is furbished with abrasive paper with a granulation starting from (P=120, P=400, P=800, P=1200).

The furbishing process is made in the presence of a water sprit, in order to eliminate the particles remaining after the furbishing process.

The following step is furbishing on the felt, with a diamond paste solution, beginning from 9[micro]m, 6[micro]m, 3[micro]m, 2[micro]m, 1[micro]m, 0,25 [micro]m, afterwards the sample is washed with ethyl alcohol.

After this process, the sample is influenced as following: for aluminium alloys it is made a stream of [H.sub.2][O.sub.2] and HF, for steel is made with ethyl alcohol (ethanol) 98% and HN[O.sub.3], and it is named nital 2%.

[FIGURE 1 OMITTED]

In order to be characterized, dissimilar braze welding joining using CMT process, were put under macro and microscopic analysis.

The macroscopic image of these combinations reveals the appearance of a thermo area, in the base materials.

This thermo influenced area is much more extended in the case of the combinations obtained through braze welding CMT of samples 1 and 4, comparing to the other samples.

At microscopic level, it is detected that in the thermo influenced area, the zinc layer is wasted from the surface of the galvanized steel, without observing an obvious change of the structure.

The structure of the base material, is formed from polyhedral ferrite granulate, to the limit of which also appear tertiary cementite precipitancy, evidenced by the halving of granulate limits (figure 1).

At none of the 5 samples is observed a change of structure due to the heating during the CMT combination process.

The microscopic analysis of joining reveals a structure composed of solid potion a, which becomes dendrite aspect and coarse particles of [Al.sub.3][Mg.sub.2], which are disposed at the limit of granule. It has to be mentioned that the precipitation phase [Al.sub.3][Mg.sub.2], at the limit of granule, maximizes the alloy's fragility Al-Mg.

3. MECHANIC ATTEMPTS OF DISSIMILAR JOINING BOARDS GALVANIZED--BOARDS MADE OF ALUMINIUM ALLOY

The results of the mechanic attempts for samples 1, 2, 3, 4, 5 are presented in table 4. For these samples the mechanic characteristics of resistance ([F.sub.max] and [R.sub.m] resistance to breakage) have raised values [F.sub.max]=3,16KN and [R.sub.m,med]=91,9 Mpa. This shows a proper accomplishment of the combined welding process.

In figure 2 is presented the curve representative for tasks 15 from which it can be observed the elongation and the breakage force. The tasks have been put to attempts to traction, with the traction installation.

[FIGURE 2 OMITTED]

4. CONCLUSION

The accuracy of the obtained results proves the quality of the CMT joining technology and indirectly the economic effects provided by the cost decreasing becomes a very important market element (Izvercian, 2002). In a global competitive world, it is very important to obtain relative and competitive advantages (Vartolomei, 2007) and this project can provide them.

A complex experimental programme has been developed for the dissimilar combinations with the assistance of the CMT process (Popescu et al., 2008).

The results of the attempts of traction, and also the analysed microstructures, have demonstrated the superiority of the CMT joining process.

The results are originally developed in the frame of the faculty, using trial programs, and using trial equipments of UPT laboratory Renar authorized. The main purpose of this research is to develop the joining technology obtained and to use it in automotive industry with real economic effects.

5. REFERENCES

Bruckner, J. (2005). Cold metal transfer has a future joining steel to aluminium, Welding Journal, Vol. 84, No. 6, June, 2006, pp. 38-40, ISSN 0043-2296

Izvercian, M. (2002). "Marketing Elements"; Solness Publisher, ISBN 973-8472-19-9, Timisoara

Lutz, W. (2007). Hot exhaust component perfectly "cold" welded with a robot, Praktiker, Vol. 59, no. 5, May, 2007, pp. 162-164, ISSN: 0554-9965

Popescu, M.; Magda, A.; Mocuta, GE.; Demian, C.; Perianu, IA. & Groza, D. (2008). Comparative approach of MIG/MAG Brazing and CMT galvanized steel joining processes for automotive applications, Scientific Bulletin of the Politehnica University of Timisoara Transactions on Mechanics, Popescu (Ed.) Fasc. 2, Tom 53(67), pp. 29-36, Editura Politehnica, ISSN 1224-6077, Timisoara

Staubach, M. (2007). Joining of steel-aluminium dissimilar joints with low energy GMA process and filler materials based on aluminium and zinc, Schweissen und Schneiden, Vol. 59, No. 6, June, 2007, pp. 302, 304-310, 312-313, ISSN: 0036-7184

Staubach, M (2008). Joining of steel-aluminium mixed joints with energy reduced GMA processes and filler materials on an aluminium and zinc basis, Welding and Cutting, Vol. 7, No 1, Jan, 2007, pp. 30-34, ISSN: 0036-7184

Vartolomei, M. (2007). The Relative Advantage Through Romanian European Integration Process, Recent Journal Vol.8, No 3a(21a), November 2007, pp.367-370, ISSN 1582-0246

Tab. 1. Welding parameters through CMT process

Is Ua s [mm] ds Wire Gas Gas
[A] [V] [mm] type protection flow

40 10.7 1,5Al, 1,25 1.2 AlMg AlMg3 10
 galvanized steel 3 l/min

56 11.5 1,5Al, 1,25 1.2 11
 galvanized steel l/min

50 11.4 1,5Al, 1,25 1.2 10
 galvanized steel l/min

51 11.4 1,5Al, 1,25 1.2 10
 galvanized steel l/min

62 11.8 3 Al, 1,25 1.2 12
 galvanized steel l/min

Tab. 2. Percentage concentration board alloy aluminium

Percentage 1 2 3 Sum of Medium
concentration determin square
 ations deviation

Al 96.25 96.48 96.29 96.34 0.1231
Si 0.1694 0.1769 0.1721 0.1728 0.0038
Fe 0.2558 0.2424 0.2484 0.2489 0.0067
Cu 0 0 0 0 0
Mn 0.3146 0.3082 0.3112 0.3114 0.0032
Mg 2.903 2.686 2.863 2.817 0.1158
Cr 0 0 0 0 0
Zn 0 0 0 0 0
Ti <0.009 <0.006 <0.010 <0.008 0.0024

Tab. 3. Percentage concentration board steel

Percentage 1 2 3 4
concentration

99.51 99.52 99.53 99.53 99.52
0.0607 0.0633 0.0565 0.0568 0.0593
0.0269 0.0148 0.0136 <0.007 <0.015
0.1931 0.187 0.1909 0.1876 0.1897
0 0 0 0 0
<0.000 <0.002 <0.00 <0.000 <0.000
0.0107 0.0148 0.0123 0.0137 0.0129
0.0140 0.0141 <0.009 <0.009 <0.011
0.0182 0.0216 0.0175 0.0435 0.0252
0.0175 0.0229 0.0163 0.0166 0.0183
0.0389 0.0388 0.0519 0.0344 0.0410
<0.003 <0.003 <0.001 <0.003 <0.002
<0.002 <0.001 <0.002 <0.000 <0.001
<0.000 <0.00 <0.00 <0.000 <0.000
<0.000 <0.00 <0.00 <0.000 <0.000
<0.000 <0.00 <0.00 <0.000 <0.000

Percentage Sum of Medium
concentration determinations square
 deviation

99.51 0.0072 99.51
0.0607 0.0033 0.0607
0.0269 0.0082 0.0269
0.1931 0.0029 0.1931
0 0 0
<0.000 0.0011 <0.000
0.0107 0.0018 0.0107
0.0140 0.0025 0.0140
0.0182 0.0124 0.0182
0.0175 0.0031 0.0175
0.0389 0.0075 0.0389
<0.003 0.0007 <0.003
<0.002 0.0011 <0.002
<0.000 0.0003 <0.000
<0.000 0.0002 <0.000
<0.000 0.0000 <0.000

Tab. 4. Mechanic attempts of the combination
aluminium-galvanized steel

Task Welding [F.sub.max] [F.sub.max,med]
no. dimensions [KN] [KN]

 l H
 [mm] [mm]

1 20 2 3,08 3,16
2 20 2 4,24
3 20 2 2,79
4 20 2 3,28
5 20 2 4,99

Task [R.sub.m] [R.sub.m,med]
no. [Mpa] [Mpa]

1 77 91,90
2 106
3 69,75
4 82
5 124,75