**2. Importance of microstructure and mechanical properties on aluminum welds**

After welding, the microstructure and mechanical properties conditions are the principal aspects that determine the appropriate perform in structures and components of aluminum alloys. It means that it is necessary to know exactly the mechanical behavior of the welded joint, including the global and local mechanical properties. This is necessary because the temperature susceptibility of some aluminum alloys tends to change in a great manner the microstructure conditions in the fusion zone and in the HAZ. Here are some results on the

temperature field, cooling rate, *x*-direction force, torque and power are totally depended of the welding speed, the tool rotation speed, the vertical pressure on the tool, etc. Figure 8, shows a relationship between rotational speed and peak temperature in FSW of a 6063

FSW enables long lengths of weld to be made without any melting taking place. This provides some important metallurgical advantages compared with fusion welding, i.e. no melting means that solidification and liquation cracking are eliminated; dissimilar alloys can be successfully joined; the stirring and forcing action produces a fine-grain structure. However, one disadvantage is that the keyhole (exit hole) remains when the tool is retracted

Several alloys have been welded by FSW, they included the following aluminum alloys:

Although, welding of aluminum alloys is relatively easy employing friction stir welding, when the thickness is thick a fusion welding process is usually required to join these materials. In the case of a fusion welding process, a large amount of heat input can be dissipated via heat conduction throughout the base material close to the welded zone. Typically, this thermal dissipation induces localized isothermal sections where the thermal gradient can have important and detrimental effects on the microstructure and therefore on the mechanical properties of the material constituting the heat affected zone (HAZ), specially in aluminum alloys hardening by artificial ageing (Myhr et al., 2004). In order to improve the mechanical and microstructural conditions of the welded joint in aluminum alloys, the Modified Indirect Electric Arc (MIEA), has been developed (Ambriz at al., 2006, Ambriz et al. 2008). This welding technique is based on a simple joint modification which provided several advantages with respect to the traditional arc fusion welding process, for instance: i. The high thermal efficiency that allows welding plates by using a single welding pass. As a result, the thermal effect is reduced and the mechanical properties of the HAZ are

ii. The dilution percent of the weld pool is higher; which tends to improve the hardening effect after performing a post weld heat treatment (PWHT) (Ambriz et al., 2008), iii. The solidification mode promotes an heterogeneous nucleation and jointly diminishes

iv. The geometry of the welding profile improves the fatigue performance of the welded

MIEA welding technique employs the same equipment that is required to weld by GMAW.

After welding, the microstructure and mechanical properties conditions are the principal aspects that determine the appropriate perform in structures and components of aluminum alloys. It means that it is necessary to know exactly the mechanical behavior of the welded joint, including the global and local mechanical properties. This is necessary because the temperature susceptibility of some aluminum alloys tends to change in a great manner the microstructure conditions in the fusion zone and in the HAZ. Here are some results on the

**2. Importance of microstructure and mechanical properties on aluminum** 

5083, 5454, 6061, 6082, 2014, 2219 and 7075 (Nandan et al., 2008).

**1.5 Modified indirect electric arc welding technique (MIEA)** 

improved as compared to a multi-pass welding procedure,

A schematic representation of the MIEA joint is present in Figure 9.

aluminum alloy (Nandan et al., 2008).

at the end of the joint (Figure 7b).

the micro-porosity formation,

joint (Ambriz et al., 2010a).

**welds** 

microstructural and mechanical conditions in welding of aluminum alloys, especially for FSW and MIEA.

Fig. 9. Schematic representation of MIEA welding technique
