*4.2.2 Bonding time and temperature*

TLP diffusion bonding is a heavily time-dependent process with the duration of each stage contributing to the length of time required to achieve bond strength. Several models have been developed based on Fick's second law that seeks to predict the duration of each stage of the TLP bonding process. The most notable of these models was proposed by Zhou et al. [54]. Experimental research on TLP bonding of

#### **Figure 15.**

*(A) TLP bonding of Mg-AZ31) and Al-1100 using a Cu coating containing nano-Al2O3 particles and bonding condition 10 minutes at 500°C and 0.2 MPa (B) EDS analysis of the highlighted region.*


**97**

*Dissimilar Welding and Joining of Magnesium Alloys: Principles and Application*

magnesium alloys suggests that this model is still an important tool for predicting

Similarly, temperature serves as an important parameter in order to produce a successful joint in the diffusion bonding as it significantly changes the kinetics of the atomic movement at the interface. Given that the interlayer melts and then solidifies at the bonding temperature and therefore, the bonding temperature should reach the melting temperature of the interlayer. The temperature used should be controlled and remain constant throughout the bonding process in order to enhance diffusion, but not cause metallurgical changes or cause excess melting of the joint region. Light metals, such as magnesium, need to be bonded at an optimal

Bonding time is a variable closely related to temperature. Increasing the bonding temperature require a shorter hold time. It is seen that increasing pressure, time and temperature produces strong joint up to a point after which the parameters become redundant. The process of diffusion bonding uses a wide range of bonding time,

Long bonding times enhances atomic diffusion along the bond line but may increase the likelihood of IMCs forming at the interface, which are detrimental to mechanical properties. Research by Sun et al. [3] proved the influence of bonding temperature on shear and bonding strengths of the bonded joints followed by the pressure applied, holding time and surface roughness. Azizi and Alimardan [55] confirmed a direct proportion relationship existed between the increase in the width of the interface as the bonding temperature and hold time increases.

The properties of magnesium alloys allow them to be used in the various structural applications including biomedical applications such as implants. Given that that magnesium is non-toxic, biocompatible and biodegradable, these materials can be used to serve as implants or replacements of body tissues. The current use of titanium implants for bone treatment and implants in the tissues may be replaced by Mg alloys since titanium alloys are not biodegradable therefore another operation/surgery is needed in most cases after the healing of the affected tissues. One direction is to develop new Mg alloys with various alloying elements such as Zn, Al, Zr, and others, in order to reach the desired degradation rate suitable for the human body. Another challenge in using Mg alloy for bone fixation is the low mechanical

A significant challenge, however, is identifying suitable joining technologies capable of welding/joining magnesium to other metals such as Ti and prevents IMC formations. While conventional fusion welding is also capable of a selective dissimilar joining of Mg alloys the product of these processes is not suitable for biomedical applications. On the other hand, soli-state diffusion bonding, TLP diffusion bonding process and friction stir welding have demonstrated greatest potential for the

*DOI: http://dx.doi.org/10.5772/intechopen.85111*

the duration of each stage of the bonding process.

temperature so that micro-deformation is avoided.

from seconds to hours, for different joining surfaces.

**5. General remarks**

strength of Mg when compared to Ti.

dissimilar joining of Mg alloys.

#### **Table 1.**

*Shear strength of diffusion bonded joints.*

#### *Dissimilar Welding and Joining of Magnesium Alloys: Principles and Application DOI: http://dx.doi.org/10.5772/intechopen.85111*

magnesium alloys suggests that this model is still an important tool for predicting the duration of each stage of the bonding process.

Similarly, temperature serves as an important parameter in order to produce a successful joint in the diffusion bonding as it significantly changes the kinetics of the atomic movement at the interface. Given that the interlayer melts and then solidifies at the bonding temperature and therefore, the bonding temperature should reach the melting temperature of the interlayer. The temperature used should be controlled and remain constant throughout the bonding process in order to enhance diffusion, but not cause metallurgical changes or cause excess melting of the joint region. Light metals, such as magnesium, need to be bonded at an optimal temperature so that micro-deformation is avoided.

Bonding time is a variable closely related to temperature. Increasing the bonding temperature require a shorter hold time. It is seen that increasing pressure, time and temperature produces strong joint up to a point after which the parameters become redundant. The process of diffusion bonding uses a wide range of bonding time, from seconds to hours, for different joining surfaces.

Long bonding times enhances atomic diffusion along the bond line but may increase the likelihood of IMCs forming at the interface, which are detrimental to mechanical properties. Research by Sun et al. [3] proved the influence of bonding temperature on shear and bonding strengths of the bonded joints followed by the pressure applied, holding time and surface roughness. Azizi and Alimardan [55] confirmed a direct proportion relationship existed between the increase in the width of the interface as the bonding temperature and hold time increases.
