There is always the option to replace 6061 with 6261. Although these two alloys would appear quite similar in many ways, there is some scope to differentiate between the two. One of the differences between the two alloys is the significantly higher Mn content of 6261 compared to 6061. Alloy 6061 has I119 potential for a much greater Cr addition; however, Cr is reported [12] to have 8 much greater (negative) impact on extrudability than Mn. Therefore, the level of Cr is normally kept at the bottom end of the compositional range. It is not unusual for the Mn content of 6061 to exceed that of Cr. Plant trials using hollow sections (with a wall thickness of 1.8 mm) were con- ducted by Musulin and Dietz [6] and demonstrated that 6061 was slightly less _ sensitive to press quench rates. _This can be attributed to the higher Mn content of 6261. High excess Si alloys There are a number of high excess Si alloys available, but they ditfer in the balance between Mg2Si, excess Si, toughening elements and Cu additions. Additionally, the homogenization practice will contribute to the effectiveness of dispersoids. The applications for 6351 and 6082 are quite similar to 6061 in heavy-duty structural sections. These alloys are also more suitable for forging applications as they have lower (surface) grain coarsening susceptibility than 6061. The applications for which 6005A are suited include profiles such as flag poles, ladder parts and as a medium strength alternative to 6061 for light sections (for example, sotne light yacht mast sections). The extrusion speeds for 6005A are superior to 6061 and the alloy is more suited to thin wall sections due to its lower flow stress. Alloys 6351/6082 . The composition of 6351 and 6082 alloys contain a Mn level far in excess of other medium strength alloys such as 6061, 6261 and even 6005A. The two alloys are essentially the same in terms of major alloying additions (Mg/Si/Mn), the only differences being a higher minimum for Mg in 6082 and a greater potential for Cr additions. Additionally. the minimum T6 mechanical properties of these alloy are quite similar. The mechanical properties of alloys 6351/6082 are quite similar to the more balanced alloys such as 6061 (and 6261). The major differences between these alloys and balanced alloys are lower Mg,Si levels. higher excess Si levels, very high level of Mn and a lower Cu level. The overlap in Mg and Si levels for alloys 6061 and 6082 emphasizes these significant compositional differences (Fig. 6.6). The strengthening mechanism of these alloys could be further enhanced by Cu additions (such as the levels added to 6061). However. additions of Cu to alloys with high Si excesses is reported to reduce corrosion resistance [10] and this limits the Cu addition to 0.10%.