**3.5 Sintered densities of the resultant aluminum alloys**

**Figure 6** presents the sintered densities of pure Al and 1.5, 2, and 2.5 wt.% Sn containing Al alloys. Based on the findings, the densification of pure Al was found to enhance from 2.083 g/cm3 to 2.5397 g/cm3 , 2.573 g/cm3 and 2.575 g/cm3 , with the addition of Sn content from 1.5 to 2 wt. % and 2.5 wt.%, respectively. A comparable observation was documented in previous literature [23–24, 26, 30]. The low sintered density value of pure Al might be due to the noticeable appearance of individual particles and large number of pores formation hence portraying poor sintering response as evidenced in **Figure 5(d)**. In contrast, the addition of a higher amount of Sn reduced micro pores formation and diminished particle boundaries, which improved the sintered densities as shown in **Figure 5(b–d)**. Moreover, the lessened appearance of elongated pores might have promoted the densification effects in the current study. According to Ozay et al. [24], enhanced densification might be the result of filled gaps between the powder particles through the action of molten Sn, which also contributed to reduced porosity. Furthermore, Sercombe et al. [13] suggested that improved wetting effects with the implementation of higher Sn content led to reduced surface tension as Sn dispersed into the liquid phase during sintering. Atabay et al. [31] also highlighted that the existence of Mg2Sn intermetallic compounds contributed to the positive effects of densification of the Al alloys. Therefore, the highest sintered density of the Al alloys was observed when 2.5 wt.% of Sn was added. This is further supported by the higher and more intense visible XRD peaks of the intermetallic compounds compared to the pure Al and Al alloys with 1.5 wt.% of Sn as demonstrated in **Figure 7(c)**.

#### **3.6 Compressive strength of resultant aluminum alloys**

A compressive test was conducted to evaluate the response of the pure Al and 1.5, 2, and 2.5 wt.% Sn containing Al alloys under a compressive load. The stress-strain curve of the resultant pure Al and Al alloys with varying Sn content is shown in **Figure 7**. The obtained stress-strain curve of the pure Al and Al alloys *Assisting Liquid Phase Sintering of Pure Aluminum (Al) by the Tin Addition DOI: http://dx.doi.org/10.5772/intechopen.101507*

**Figure 9.** *Compressive yield strength of pure Al and Al alloys with different Sn content of 1.5, 2, and 2.5 wt.%.*

obeyed the typical stress-strain curve of Al and its alloys. To better understand, the compressive yield strength of the pure Al and Al alloys is displayed in **Figure 9**. Based on the findings, the compressive yield strength of the pure Al demonstrated the lowest yield strength value of 10.31 MPa, implying poor sintering response owing to the presence of individual particles with greater number of pores formation as seen in **Figure 5(d)**. This shows that the absence of Sn as sintering additive in combination with Mg constituent was unfavorable in promoting the liquid phase sintering of pure Al. On the other hand, Al alloys exhibited an increasing trend from 42.72 to 47.27 MPa with the Sn content of 1.5 and 2 wt.%, respectively. However, the addition of 2.5 wt.% Sn (the highest) reduced the compressive yield strength of the Al alloys from 47.27 (2 wt.% Sn) to 44.21 MPa. Therefore, the results were inconsistent with the results from the sintered density measurements, presumably due to a slightly increased particle boundary or grain coarsening, as revealed in **Figure 5(c)**. Furthermore, parallel observations were also discussed by Padmavathi and Upadhyaya [26].

Although the presence of Mg2Sn compounds (**Figure 8**(**b** and **c**)) produced substantial improvements in the mechanical performance of Al and its alloys, the effects of grain coarsening were more pronounced, which reduced the compressive yield strength of the Al alloys when the Sn content was maximized to 2.5 wt.% [31]. Moreover, it was reported that excessive content of Sn caused undiffused liquid phase to remain at the particle boundary and led to the brittle creation of particle boundary networks, that consequently reduced the mechanical performance of Al and its alloys [13, 31, 17–19]. Therefore, it could be hypothesized that particle boundary enlargement and liquid phase profusion might contribute to the decreased compressive strength of the Al alloys that were fabricated in the current study.

### **4. Conclusion**

The utilization of Sn element that served as sintering additive in the current study significantly improved the sintering response of the resultant Al alloys that were fabricated via powder metallurgy technique. The varying Sn content between 1.5, 2, and 2.5 wt.% enhanced the properties of the resultant Al alloys in terms of their physical appearance, from black to sliver-like coloring due to oxidation-reduction, and sintered densities from 2.5397 to 2.575 g/cm3 as the gaps between particles were filled by molten Sn, which lessened pore formation and appearance of particle boundary. Therefore, the microstructure of the resultant Al alloys confirmed the pore rounding and diminished particle boundary that led to the improved metallurgical bonding between the Al particles.

Additionally, the compressive yield strength of the resultant Al alloys increased from 42.72 to 47.27 MPa with an increased amount of Sn (from 1.5 to 2 wt.%), which were the result of diminished particle boundary and reduced pores formation. However, despite a positive increment in the sintered density of the Al alloys with increased Sn content of up to 2.5 wt.%, the compressive yield strength was slightly reduced. The finding might be attributed to the excessive liquid phase formed along with the visible appearance of particle boundary or grain coarsening. In conclusion, the study showed that the addition of Sn as sintering additive successfully promoted the Al alloys liquid phase sintering, especially with increased Sn content.
