Drilled surface of light metals (pure aluminum and aluminum alloys) are rougher than that of steels of iron. This fact would be explained that cutting conditions are changed with the depth of cut owing to generation of cutting heat and formation of deposits. In cutting of pure aluminum plate, it is impossible to cut the depth of more than 23 times as large as the drilling diameter.
This paper discusses machinability in drilling for five kinds of materials (1100-O, 24S-T4, 5086-O, K56S-F, and 11S-T3) having thicknesses of 3 values (10, 20 and 30 mm).
The experiments were made in three types of drilling (4 and 10 mmφ drilling, and 10 mmφ drilling after 4 mmφ pre-drilling)by using two kinds of tools (4 and 10 mmφ drills).
Then machinability and cutting phenomena were discussed in connection with measured values of cutting force which changed with progress of drilling, depth of deformed layer, contact area between clearance flank of cutting edge and material and profile of chips.
The results obtained by the experiments were as follows:
(1) Except for pure aluminum, cutting forces (both thrust and torque) were proportional to hardness of work piece and increased with feeding speed; however, they did not depend on cutting speed.
(2) In pure aluminum, cutting force increased with feeding speed. The effects of cutting conditions were greater on torque rather than thrust; in particular, thickness of work piece had great effects on thrust.
(3) Independcnt of the plate thickness, in drilling of 1100-O, 24S-T4, and 11S-T3, transitional phenomena of cutting force were observed in some place at a time more delayed with the increase of cutting and feeding speeds.
(4) In pure aluminum, the depth of deformed layer increased and varied with the progress of drilling.

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Effects of addition of Mg (0.11.2wt%) to Al-Si-Cu alloys on the impact strength and structures were examined by means of Charpy impact test and metallographic method.
The following four types of specimens were used for the experiments.
(a) As cast.
(b) Solution treated at 500°C for 240 min.
(c) Age hardened at 160°C for 300 min. after solution treatment.
(d) Age hardened at 200°C for 300 min. after casting.
The results obtained were as follows:
(1) The impact strength of Al-Si-Cu alloys containing Mg was much increased by solution treatment at 500°C for 240 min. as observed in Al-Si and Al-Si-Cu alloys. The behavior of impact rupture was characterized by a great increase in time for formation and propagation of cracks with a small increase in maximum load, which resulted in a great increase in impulse. The above behavior would be attributed to the dissolution of Cu and Si into matrix and the changes in shape and amount of crystallites.
(2) The impact strength of as cast and solution treated alloys were likely to be decreased with the increase in Mg content. The behavior of impact rupture was characterized by a decrease in time for formation and propagation of cracks with a constant maximum load. The above behavior would be attributed to the increase in remaining undissolved crystallites due to the addition of Mg.
(3) The impact strength of the alloys age hardened at 160°C for 300 min. after solution treatment and those age hardened at 200°C For 300 min. after casting were likely to be decreased with the increase in Mg content.
The above behavior of impact rupture was characterized by the decrease in time for formation and propagation of cracks with the increase in maximum load, which led to the decrease in impulse. The behavior of the former alloys would be attributed to the composite effect of changes in both of shape and amount of crystallites (as described in (1)) and age hardening. Therefore, the increase in maximum load would be attributed to the effect of age hardening.
(4) It was found that the hardness of Al-Si-Cu-Mg alloys after ageing was not different between the specimen age hardened at 200°C for 300 min. after casting and that age hardened at 160°C for 300 min, after solution treatment, but the impact strength was much different between the both. It was observed by fractography that the former specimen showed brittle fracture and the latter showed ductile fracture, though they had the same composition and hardness.

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Al-Mg(68%) alloy ingots containing small amounts of Mn and/or Cr were prepared in a melting-casting apparatus protected by argon atmosphere.
Macrostructure, grain size, hardness and density of dispersed fine particles were examined on the plate specimens of the ingot.
X-ray pole figure was also examined on the sheets containing 5%Mg and small amounts of Mn and Cr.
The results obtained were as follows:
(1) There were upper and lower limits of Mg content in abnormal grain growth of Al-Mg alloys.
(2) The limits were explained from the relation between the initial grain growth and the density of dispersed fine particles, according to M. Hillbert's Theory on abnormal grain growth.
(3) The aggregate structure of secondary recrystallization of 5056 alloy sheets were found to be composed of (110) [111], (001) [110], (113) [110] and (hkl) [110] planes.

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Binary Mg alloys containing any one of zinc, lead, tin, indium, thallium, cadmium, yttrium, gallium and lanthanum were prepared in a melting-casting apparatus protected by sulfur dioxide atmosphere.
Corrosion rates of the polished specimens of these alloys in 3%NaCl aq. solution (at 30°C) were measured and the following results were obtained.
(1) Zn (≤4%) and Pb (≤1%) had good effects on corrosion resistance.
(2) Sn (≤7%), In (≤0.1%), Y (≤1%), Ga (≤5%) and Cd (≤7%) had no effects on corrosion resistance.
(3) Pb (≥5%) and La (0.5%) had slightly detrimental effects and Tl (≥0.5%), In (≥6%), La (≥1%) and Cd (≥14%) extremely injurred the corrosion resistance.

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Drilling machinability test was carried out on Al-Si binary alloys containing 1about 30% of Si. The tool used for the experiments was a drill of the standard type of 5mm in diameter.
The time and energy in watt for drilling a predetermined depth was decreased with the increase in Si content; however, there was a maximum at 1013% of Si content.The relation between the drilling time and Si conformed to the fragments of chips. Therefore, the improvement in machinability with increasing Si content would greatly depend upon chip treatments. The machinability was decreased by spherodizing of eutectic Si plate crystals. This tendency was particularly evident in low Si content.
In conclusion, it was considered that the drilling machinability was improved by the presence of two phases of proper structres.

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